[svn-r5760] Purpose:

    New features, etc.

Description:
    Bring over all the recent changes from the release branch.

Platforms tested:
    IRIX64 6.5 (modi4) w/parallel

3 files changed, 803 insertions, 507 deletions

diff --git a/perform/pio_engine.c b/perform/pio_engine.c
index a9499d3..126d88a 100644
--- a/perform/pio_engine.c
+++ b/perform/pio_engine.c
@@ -45,9 +45,9 @@
 
 /* sizes of various items. these sizes won't change during program execution */
 /* The following three must have the same type */
-#define ELMT_SIZE           (sizeof(int))          /* we're doing ints */
-#define ELMT_MPI_TYPE       MPI_INT
-#define ELMT_H5_TYPE        H5T_NATIVE_INT
+#define ELMT_SIZE           (sizeof(unsigned char))     /* we're doing bytes */
+#define ELMT_MPI_TYPE       MPI_BYTE
+#define ELMT_H5_TYPE        H5T_NATIVE_UCHAR
 
 #define GOTOERROR(errcode)	{ ret_code = errcode; goto done; }
 #define GOTODONE		{ goto done; }
@@ -130,6 +130,7 @@ static herr_t do_fclose(iotype iot, file_descr *fd);
 static void do_cleanupfile(iotype iot, char *fname);
 
 /* GPFS-specific functions */
+#ifdef H5_HAVE_GPFS
 static void access_range(int handle, off_t start, off_t length, int is_write);
 static void free_range(int handle, off_t start, off_t length);
 static void clear_file_cache(int handle);
@@ -137,6 +138,7 @@ static void cancel_hints(int handle);
 static void start_data_shipping(int handle, int num_insts);
 static void stop_data_shipping(int handle);
 static void invalidate_file_cache(const char *filename);
+#endif /* H5_HAVE_GPFS */
 
 /*
  * Function:    do_pio
@@ -156,12 +158,12 @@ do_pio(parameters param)
     iotype      iot;
 
     char        fname[FILENAME_MAX];
-    int         maxprocs;
-    long	nfiles, nf;
+    long	nf;
     long        ndsets;
-    off_t       nelmts;
+    off_t       nbytes;                 /* Number of bytes per dataset  */
     char        *buffer = NULL;         /*data buffer pointer           */
     size_t      buf_size;               /*data buffer size in bytes     */
+    size_t      blk_size;               /*data block size in bytes      */
 
     /* HDF5 variables */
     herr_t          hrc;                /*HDF5 return code              */
@@ -190,16 +192,15 @@ do_pio(parameters param)
         GOTOERROR(FAIL);
     }
 
-    nfiles = param.num_files;       /* number of files                      */
     ndsets = param.num_dsets;       /* number of datasets per file          */
-    nelmts = param.num_elmts;       /* number of elements per dataset       */
-    maxprocs = param.num_procs;     /* max number of mpi-processes to use   */
+    nbytes = param.num_bytes;       /* number of bytes per dataset          */
     buf_size = param.buf_size;
+    blk_size = param.blk_size;
 
-    if (nfiles < 0 ) {
+    if (param.num_files < 0 ) {
         fprintf(stderr,
                 "number of files must be >= 0 (%ld)\n",
-                nfiles);
+                param.num_files);
         GOTOERROR(FAIL);
     }
 
@@ -210,26 +211,51 @@ do_pio(parameters param)
         GOTOERROR(FAIL);
     }
 
-    if (maxprocs <= 0 ) {
+    if (param.num_procs <= 0 ) {
         fprintf(stderr,
                 "maximum number of process to use must be > 0 (%d)\n",
-                maxprocs);
+                param.num_procs);
         GOTOERROR(FAIL);
     }
 
-    /* allocate transfer buffer */
+    /* Validate transfer buffer size & block size*/
+    if(blk_size<=0) {
+        HDfprintf(stderr,
+	    "Transfer block size (%Hd) must be > 0\n", (long_long)blk_size);
+	GOTOERROR(FAIL);
+    }
     if(buf_size<=0) {
         HDfprintf(stderr,
 	    "Transfer buffer size (%Hd) must be > 0\n", (long_long)buf_size);
 	GOTOERROR(FAIL);
-    }else{
-        buffer = malloc(buf_size);
+    }
+    if ((buf_size % blk_size) != 0){
+        HDfprintf(stderr,
+            "Transfer buffer size (%Hd) must be a multiple of the "
+            "interleaved I/O block size (%Hd)\n",
+            (long_long)buf_size, (long_long)blk_size);
+        GOTOERROR(FAIL);
+    }
+    if((nbytes%pio_mpi_nprocs_g)!=0) {
+        HDfprintf(stderr,
+            "Dataset size (%Hd) must be a multiple of the "
+            "number of processes (%d)\n",
+            (long_long)nbytes, pio_mpi_nprocs_g);
+	GOTOERROR(FAIL);
+    }
+    if(((nbytes/pio_mpi_nprocs_g)%buf_size)!=0) {
+        HDfprintf(stderr,
+            "Dataset size/process (%Hd) must be a multiple of the "
+            "trasfer buffer size (%Hd)\n",
+            (long_long)(nbytes/pio_mpi_nprocs_g), (long_long)buf_size);
+	GOTOERROR(FAIL);
+    }
 
-        if (buffer == NULL){
-            HDfprintf(stderr, "malloc for transfer buffer size (%Hd) failed\n",
-                (long_long)buf_size);
-            GOTOERROR(FAIL);
-        }
+    /* Allocate transfer buffer */
+    if ((buffer = malloc(buf_size)) == NULL){
+        HDfprintf(stderr, "malloc for transfer buffer size (%Hd) failed\n",
+            (long_long)(buf_size));
+        GOTOERROR(FAIL);
     }
 
     if (pio_debug_level >= 4) {
@@ -242,25 +268,26 @@ do_pio(parameters param)
             fprintf(output, "Timer details:\n");
     }
 
-    for (nf = 1; nf <= nfiles; nf++) {
+    for (nf = 1; nf <= param.num_files; nf++) {
 	/*
 	 * Write performance measurement
 	 */
         /* Open file for write */
         char base_name[256];
 
-        MPI_Barrier(pio_comm_g);
-
         sprintf(base_name, "#pio_tmp_%lu", nf);
         pio_create_filename(iot, base_name, fname, sizeof(fname));
 
+	/* Need barrier to make sure everyone starts at the same time */
+        MPI_Barrier(pio_comm_g);
+
         set_time(res.timers, HDF5_GROSS_WRITE_FIXED_DIMS, START);
         hrc = do_fopen(&param, fname, &fd, PIO_CREATE | PIO_WRITE);
 
         VRFY((hrc == SUCCESS), "do_fopen failed");
 
         set_time(res.timers, HDF5_FINE_WRITE_FIXED_DIMS, START);
-        hrc = do_write(&res, &fd, &param, ndsets, nelmts, buf_size, buffer);
+        hrc = do_write(&res, &fd, &param, ndsets, nbytes, buf_size, buffer);
         set_time(res.timers, HDF5_FINE_WRITE_FIXED_DIMS, STOP);
 
         VRFY((hrc == SUCCESS), "do_write failed");
@@ -275,6 +302,10 @@ do_pio(parameters param)
             /*
              * Read performance measurement
              */
+	    /* Need barrier to make sure everyone is done writing and has
+	     * closed the file.  Also to make sure everyone starts reading
+	     * at the same time.
+	     */
             MPI_Barrier(pio_comm_g);
 
             /* Open file for read */
@@ -284,7 +315,7 @@ do_pio(parameters param)
             VRFY((hrc == SUCCESS), "do_fopen failed");
 
             set_time(res.timers, HDF5_FINE_READ_FIXED_DIMS, START);
-            hrc = do_read(&res, &fd, &param, ndsets, nelmts, buf_size, buffer);
+            hrc = do_read(&res, &fd, &param, ndsets, nbytes, buf_size, buffer);
             set_time(res.timers, HDF5_FINE_READ_FIXED_DIMS, STOP);
             VRFY((hrc == SUCCESS), "do_read failed");
 
@@ -295,6 +326,8 @@ do_pio(parameters param)
             VRFY((hrc == SUCCESS), "do_fclose failed");
         }
 
+	/* Need barrier to make sure everyone is done with the file */
+	/* before it may be removed by do_cleanupfile */
         MPI_Barrier(pio_comm_g);
         do_cleanupfile(iot, fname);
     }
@@ -447,23 +480,31 @@ pio_create_filename(iotype iot, const char *base_name, char *fullname, size_t si
  */
 static herr_t
 do_write(results *res, file_descr *fd, parameters *parms, long ndsets,
-         off_t nelmts, size_t buf_size, void *buffer)
+         off_t nbytes, size_t buf_size, void *buffer)
 {
     int         ret_code = SUCCESS;
     int         rc;             /*routine return code                   */
-    int         mrc;            /*MPI return code                       */
-    MPI_Offset	mpi_offset;
-    MPI_Status	mpi_status;
     long        ndset;
-    off_t       nelmts_xfer;
-    size_t      nelmts_toxfer;
+    size_t      blk_size;       /* The block size to subdivide the xfer buffer into */
+    off_t       nbytes_xfer;    /* Total number of bytes transferred so far */
+    size_t      nbytes_toxfer;  /* Number of bytes to transfer a particular time */
     char        dname[64];
-    off_t       dset_offset=0;    /*dataset offset in a file              */
-    off_t       file_offset;    /*file offset of the next transfer      */
-    off_t       dset_size;      /*one dataset size in bytes             */
-    size_t      nelmts_in_buf;  /*how many element the buffer holds     */
-    off_t       elmts_begin;    /*first elmt this process transfer      */
-    off_t       elmts_count;    /*number of elmts this process transfer */
+    off_t       dset_offset=0;  /*dataset offset in a file              */
+    off_t       bytes_begin;    /*first elmt this process transfer      */
+    off_t       bytes_count;    /*number of elmts this process transfer */
+    unsigned char *buf_p;       /* Current buffer pointer               */
+
+    /* POSIX variables */
+    off_t       file_offset;    /* File offset of the next transfer     */
+    off_t       posix_file_offset;    /* Base file offset of the next transfer      */
+
+    /* MPI variables */
+    MPI_Offset  mpi_file_offset;/* Base file offset of the next transfer*/
+    MPI_Offset	mpi_offset;     /* Offset in MPI file                   */
+    MPI_Datatype mpi_file_type; /* MPI derived type for file            */
+    MPI_Datatype mpi_blk_type;  /* MPI derived type for buffer          */
+    MPI_Status	mpi_status;
+    int         mrc;            /* MPI return code                      */
 
     /* HDF5 variables */
     herr_t      hrc;                    /*HDF5 return code              */
@@ -471,57 +512,146 @@ do_write(results *res, file_descr *fd, parameters *parms, long ndsets,
     hid_t       h5dset_space_id = -1;   /*dataset space ID              */
     hid_t       h5mem_space_id = -1;    /*memory dataspace ID           */
     hid_t       h5ds_id = -1;           /*dataset handle                */
-    hsize_t	h5block[1];		/*dataspace selection        */
+    hsize_t	h5block[1];		/*dataspace selection           */
     hsize_t	h5stride[1];
     hsize_t	h5count[1];
     hssize_t	h5start[1];
+    hssize_t	h5offset[1];            /* Selection offset within dataspace */
     hid_t       h5dcpl = -1;            /* Dataset creation property list */
     hid_t       h5dxpl = -1;            /* Dataset transfer property list */
 
-    /* calculate dataset parameters. data type is always native C int */
-    dset_size = nelmts * (off_t)ELMT_SIZE;
-    nelmts_in_buf = buf_size/ELMT_SIZE;
-
-    /* hdf5 data space setup */
-    if (parms->io_type == PHDF5){
-        if(nelmts>0) {
-            /* define a contiquous dataset of nelmts native ints */
-            h5dims[0] = nelmts;
-            h5dset_space_id = H5Screate_simple(1, h5dims, NULL);
-            VRFY((h5dset_space_id >= 0), "H5Screate_simple");
-        } /* end if */
-        else {
-            h5dset_space_id = H5Screate(H5S_SCALAR);
-            VRFY((h5dset_space_id >= 0), "H5Screate");
-        } /* end else */
-
-        /* Create the memory dataspace that corresponds to the xfer buffer */
-        if(nelmts_in_buf>0) {
-            h5dims[0] = nelmts_in_buf;
-            h5mem_space_id = H5Screate_simple(1, h5dims, NULL);
-            VRFY((h5mem_space_id >= 0), "H5Screate_simple");
-        } /* end if */
-        else {
-            h5mem_space_id = H5Screate(H5S_SCALAR);
-            VRFY((h5mem_space_id >= 0), "H5Screate");
-        } /* end else */
-
-        /* Create the dataset transfer property list */
-        h5dxpl = H5Pcreate(H5P_DATASET_XFER);
-        if (h5dxpl < 0) {
-            fprintf(stderr, "HDF5 Property List Create failed\n");
-            GOTOERROR(FAIL);
-        }
+    /* Get the parameters from the parameter block */
+    blk_size=parms->blk_size;
+
+    /* Prepare buffer for verifying data */
+    if (parms->verify)
+        memset(buffer,pio_mpi_rank_g,buf_size);
+
+    /* There are two kinds of transfer patterns, contiguous and interleaved.
+     * Let 0,1,2,...,n be data accessed by process 0,1,2,...,n
+     *     where n is rank of the last process.
+     * In contiguous pattern, data are accessed as
+     *    000...111...222...nnn...
+     * In interleaved pattern, data are accessed as
+     *    012...n012...n...
+     * These are all in the scope of one dataset.
+     */
+    if (parms->interleaved==0) {
+        /* Contiguous Pattern: */
+        bytes_begin = (off_t)(((double)nbytes*pio_mpi_rank_g)/pio_mpi_nprocs_g);
+    } /* end if */
+    else {
+        /* Interleaved Pattern: */
+        bytes_begin = (off_t)(blk_size*pio_mpi_rank_g);
+    } /* end else */
+
+    /* Calculate the total number of bytes (bytes_count) to be
+     * transferred by this process. It may be different for different
+     * transfer pattern due to rounding to integral values.
+     */
+    /*
+     * Calculate the beginning bytes of this process and the next.
+     * bytes_count is the difference between these two beginnings.
+     * This way, it eliminates any rounding errors.
+     * (This is tricky, don't mess with the formula, rounding errors
+     * can easily get introduced) */
+    bytes_count = (off_t)(((double)nbytes*(pio_mpi_rank_g+1)) / pio_mpi_nprocs_g)
+                  - (off_t)(((double)nbytes*pio_mpi_rank_g) / pio_mpi_nprocs_g);
+
+    /* debug */
+    if (pio_debug_level >= 4) {
+        HDprint_rank(output);
+        HDfprintf(output, "Debug(do_write): "
+            "buf_size=%Hd, bytes_begin=%Hd, bytes_count=%Hd\n",
+            (long_long)buf_size, (long_long)bytes_begin,
+            (long_long)bytes_count);
+    }
 
-        /* Change to collective I/O, if asked */
-        if(parms->collective) {
-            hrc = H5Pset_dxpl_mpio(h5dxpl, H5FD_MPIO_COLLECTIVE);
-            if (hrc < 0) {
-                fprintf(stderr, "HDF5 Property List Set failed\n");
+    /* I/O Access specific setup */
+    switch (parms->io_type) {
+        case POSIXIO:
+            /* No extra setup */
+            break;
+
+        case MPIO: /* MPI-I/O setup */
+            /* Build block's derived type */
+            mrc = MPI_Type_contiguous((int)blk_size,
+                    MPI_BYTE, &mpi_blk_type);
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_CREATE");
+
+            /* Build file's derived type */
+            mrc = MPI_Type_vector((int)(buf_size/blk_size), (int)1,
+                    (int)pio_mpi_nprocs_g, mpi_blk_type, &mpi_file_type);
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_CREATE");
+
+            /* Commit file type */
+            mrc = MPI_Type_commit( &mpi_file_type );
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_COMMIT");
+
+            /* Commit buffer type */
+            mrc = MPI_Type_commit( &mpi_blk_type );
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_COMMIT");
+            break;
+
+        case PHDF5: /* HDF5 setup */
+            if(nbytes>0) {
+                /* define a contiquous dataset of nbytes native bytes */
+                h5dims[0] = nbytes;
+                h5dset_space_id = H5Screate_simple(1, h5dims, NULL);
+                VRFY((h5dset_space_id >= 0), "H5Screate_simple");
+
+                /* Set up the file dset space id to select the pattern to access */
+                if (parms->interleaved==0){
+                    /* Contiguous pattern */
+                    h5start[0] = bytes_begin;
+                    h5stride[0] = h5block[0] = blk_size;
+                    h5count[0] = buf_size/blk_size;
+                } /* end if */
+                else {
+                    /* Interleaved access pattern */
+                    /* Skip offset over blocks of other processes */
+                    h5start[0] = bytes_begin;
+                    h5stride[0] = blk_size*pio_mpi_nprocs_g;
+                    h5block[0] = blk_size;
+                    h5count[0] = buf_size/blk_size;
+                } /* end else */
+                hrc = H5Sselect_hyperslab(h5dset_space_id, H5S_SELECT_SET,
+                          h5start, h5stride, h5count, h5block); 
+                VRFY((hrc >= 0), "H5Sselect_hyperslab");
+            } /* end if */
+            else {
+                h5dset_space_id = H5Screate(H5S_SCALAR);
+                VRFY((h5dset_space_id >= 0), "H5Screate");
+            } /* end else */
+
+            /* Create the memory dataspace that corresponds to the xfer buffer */
+            if(buf_size>0) {
+                h5dims[0] = buf_size;
+                h5mem_space_id = H5Screate_simple(1, h5dims, NULL);
+                VRFY((h5mem_space_id >= 0), "H5Screate_simple");
+            } /* end if */
+            else {
+                h5mem_space_id = H5Screate(H5S_SCALAR);
+                VRFY((h5mem_space_id >= 0), "H5Screate");
+            } /* end else */
+
+            /* Create the dataset transfer property list */
+            h5dxpl = H5Pcreate(H5P_DATASET_XFER);
+            if (h5dxpl < 0) {
+                fprintf(stderr, "HDF5 Property List Create failed\n");
                 GOTOERROR(FAIL);
+            }
+
+            /* Change to collective I/O, if asked */
+            if(parms->collective) {
+                hrc = H5Pset_dxpl_mpio(h5dxpl, H5FD_MPIO_COLLECTIVE);
+                if (hrc < 0) {
+                    fprintf(stderr, "HDF5 Property List Set failed\n");
+                    GOTOERROR(FAIL);
+                } /* end if */
             } /* end if */
-        } /* end if */
-    }
+            break;
+    } /* end switch */
 
     for (ndset = 1; ndset <= ndsets; ++ndset) {
 
@@ -532,7 +662,7 @@ do_write(results *res, file_descr *fd, parameters *parms, long ndsets,
         case POSIXIO:
         case MPIO:
             /* both posix and mpi io just need dataset offset in file*/
-            dset_offset = (ndset - 1) * dset_size;
+            dset_offset = (ndset - 1) * nbytes;
             break;
 
         case PHDF5:
@@ -545,7 +675,7 @@ do_write(results *res, file_descr *fd, parameters *parms, long ndsets,
             /* Make the dataset chunked if asked */
             if(parms->h5_use_chunks) {
                 /* Set the chunk size to be the same as the buffer size */
-                h5dims[0] = nelmts_in_buf;
+                h5dims[0] = buf_size;
                 hrc = H5Pset_chunk(h5dcpl, 1, h5dims);
                 if (hrc < 0) {
                     fprintf(stderr, "HDF5 Property List Set failed\n");
@@ -583,201 +713,191 @@ do_write(results *res, file_descr *fd, parameters *parms, long ndsets,
             break;
         }
 
-	/* There are two kinds of transfer patterns, contiguous and interleaved.
-	 * Let 0,1,2,...,n be data accessed by process 0,1,2,...,n
-	 *     where n is rank of the last process.
-	 * In contiguous pattern, data are accessed as
-	 *    000...111...222...nnn...
-	 * In interleaved pattern, data are accessed as
-	 *    012...n012...n...
-	 * These are all in the scope of one dataset.
-	 */
-	/* Calculate the total number of elements (elmts_count) to be
-	 * transferred by this process. It may be different for different
-	 * transfer pattern due to rounding to integral values.
-	 */
-	if (parms->interleaved==0) {
-	    /* Contiguous Pattern:
-	     * Calculate the beginning element of this process and the next.
-	     * elmts_count is the difference between these two beginnings.
-	     * This way, it eliminates any rounding errors.
-	     */
-	    elmts_begin = (off_t)(((double)nelmts)/pio_mpi_nprocs_g*pio_mpi_rank_g);
-
-	    /* Do not cast elmt_begin to other types, especially non-integral
-	     * types, else it may introduce rounding discrepency. */
-	    if (pio_mpi_rank_g < (pio_mpi_nprocs_g - 1))
-		elmts_count = (off_t)(((double)nelmts) / pio_mpi_nprocs_g * (pio_mpi_rank_g + 1))
-				- elmts_begin;
-	    else
-		/* last process.  Take whatever are left */
-		elmts_count = nelmts - elmts_begin;
-	} /* end if */
-        else {
-	    /* Interleaved Pattern:
-	     * Each process takes buf_size of elements, starting with the first
-	     * process.  So, the last process may have fewer or even none.
-	     * Calculate the beginning element of this process.
-	     * The elmnts_begin here marks only the beginning of the first
-	     * block accessed by this process.
-	     */
-	    /* Algorithm:
-	     * First allocate equal blocks per process, i.e. one block each
-	     * process for every block_size*nprocs.
-	     * If there is remaining unallocated, give a block each to process
-	     * starting at proc 0.  The last process may get a partial block.
-	     */ 
-	    off_t remain_nelmts, remain_begin;	/* unallocated remaining*/
-
-	    elmts_begin = (off_t)(nelmts_in_buf*pio_mpi_rank_g);
-
-	    /* must use integer calculation next */
-	    /* allocate equal blocks per process */
-	    elmts_count = (nelmts / (off_t)(nelmts_in_buf*pio_mpi_nprocs_g)) *
-			    (off_t)nelmts_in_buf;
-	    remain_nelmts = nelmts % (off_t)(nelmts_in_buf*pio_mpi_nprocs_g);
-
-	    /* allocate any remaining */
-	    remain_begin = (off_t)(nelmts_in_buf*pio_mpi_rank_g);
-	    if (remain_nelmts > remain_begin){
-		/* it gets something */
-		if (remain_nelmts > (remain_begin+(off_t)nelmts_in_buf)){
-		    /* one full block */
-		    elmts_count += nelmts_in_buf;
-		}else{
-		    /* only a partial block */
-		    elmts_count += remain_nelmts - remain_begin;
-		}
-	    }
-	}
-	/* debug */
-	if (pio_debug_level >= 4) {
-	    HDprint_rank(output);
-	    HDfprintf(output, "Debug(do_write): "
-		"nelmts_in_buf=%Hd, elmts_begin=%Hd, elmts_count=%Hd\n",
-		(long_long)nelmts_in_buf, (long_long)elmts_begin,
-		(long_long)elmts_count);
-	}
-
-
-	/* The task is to transfer elmts_count elements, starting at
-	 * elmts_begin position, using transfer buffer of buf_size bytes.
+	/* The task is to transfer bytes_count bytes, starting at
+	 * bytes_begin position, using transfer buffer of buf_size bytes.
 	 * If interleaved, select buf_size at a time, in round robin
 	 * fashion, according to number of process. Otherwise, select
-	 * all elmt_count in contiguous.
+	 * all bytes_count in contiguous.
 	 */
-        nelmts_xfer = 0 ;
-
-        /* Start "raw data" write timer */
-        set_time(res->timers, HDF5_RAW_WRITE_FIXED_DIMS, START);
+        nbytes_xfer = 0 ;
 
-        while (nelmts_xfer < elmts_count){
-	    /* transfer one buffer of data each round */
-	    /* Note: because size_t is unsigned, avoid expressions that */
-	    /* can be negative. */
-            if ((nelmts_xfer + (off_t)nelmts_in_buf) <= elmts_count) {
-                nelmts_toxfer = nelmts_in_buf;
-            } else {
-                /* last transfer of a partial buffer */
-                nelmts_toxfer = elmts_count - nelmts_xfer;
-            }
+        /* Set base file offset for all I/O patterns and POSIX access */
+        posix_file_offset = dset_offset + bytes_begin;
 
-	    if (parms->verify) {
-		/*Prepare write data for verify later*/
-                int *intptr = (int *)buffer;
-                size_t i;
+        /* Set base file offset for all I/O patterns and MPI access */
+        mpi_file_offset = (MPI_Offset)(dset_offset + bytes_begin);
 
-                for (i = 0; i < nelmts_toxfer; ++i)
-                    *intptr++ = pio_mpi_rank_g;
-            }
+        /* Start "raw data" write timer */
+        set_time(res->timers, HDF5_RAW_WRITE_FIXED_DIMS, START);
 
+        while (nbytes_xfer < bytes_count){
             /* Write */
             /* Calculate offset of write within a dataset/file */
             switch (parms->io_type) {
             case POSIXIO:
-		if (parms->interleaved==0) {
-		    /* Contiguous pattern */
-		    /* need to (off_t) the elmnts_begin expression because they */
-		    /* may be of smaller sized integer types */
-		    file_offset = dset_offset + (off_t)(elmts_begin + nelmts_xfer)*(off_t)ELMT_SIZE;
-		} /* end if */
-                else {
-		    /* Interleaved access pattern */
-                    /* Skip offset over blocks of other processes */
-                    file_offset = dset_offset +
-                        (off_t)(elmts_begin + (nelmts_xfer*pio_mpi_nprocs_g))*(off_t)ELMT_SIZE;
-		} /* end else */
-
-                /* only care if seek returns error */
-                rc = POSIXSEEK(fd->posixfd, file_offset) < 0 ? -1 : 0;
-                VRFY((rc==0), "POSIXSEEK");
-                /* check if all bytes are transferred */
-                rc = ((ssize_t)(nelmts_toxfer*ELMT_SIZE) ==
-                    POSIXWRITE(fd->posixfd, buffer, nelmts_toxfer*ELMT_SIZE));
-                VRFY((rc != 0), "POSIXWRITE");
-                break;
-
-            case MPIO:
-		if (parms->interleaved==0){
-		    /* Contiguous pattern */
-                    mpi_offset = dset_offset + (elmts_begin + nelmts_xfer)*(off_t)ELMT_SIZE;
+                /* Contiguous pattern */
+                if (parms->interleaved==0) {
+                    /* Compute file offset */
+                    file_offset = posix_file_offset + (off_t)nbytes_xfer;
+
+                    /* only care if seek returns error */
+                    rc = POSIXSEEK(fd->posixfd, file_offset) < 0 ? -1 : 0;
+                    VRFY((rc==0), "POSIXSEEK");
+
+                    /* check if all bytes are written */
+                    rc = ((ssize_t)buf_size ==
+                        POSIXWRITE(fd->posixfd, buffer, buf_size));
+                    VRFY((rc != 0), "POSIXWRITE");
+
+                    /* Advance global offset in dataset */
+                    nbytes_xfer+=buf_size;
                 } /* end if */
+                /* Interleaved access pattern */
                 else {
-		    /* Interleaved access pattern */
-                    /* Skip offset over blocks of other processes */
-                    mpi_offset = dset_offset + (elmts_begin + (nelmts_xfer*pio_mpi_nprocs_g))*(off_t)ELMT_SIZE;
+                    /* Set the base of user's buffer */
+                    buf_p=(unsigned char *)buffer;
+
+                    /* Set the number of bytes to transfer this time */
+                    nbytes_toxfer = buf_size;
+
+                    /* Loop over the buffers to write */
+                    while(nbytes_toxfer>0) {
+                        /* Skip offset over blocks of other processes */
+                        file_offset = posix_file_offset +
+                            (off_t)(nbytes_xfer*pio_mpi_nprocs_g);
+
+                        /* only care if seek returns error */
+                        rc = POSIXSEEK(fd->posixfd, file_offset) < 0 ? -1 : 0;
+                        VRFY((rc==0), "POSIXSEEK");
+
+                        /* check if all bytes are written */
+                        rc = ((ssize_t)blk_size ==
+                            POSIXWRITE(fd->posixfd, buf_p, blk_size));
+                        VRFY((rc != 0), "POSIXWRITE");
+
+                        /* Advance location in buffer */
+                        buf_p+=blk_size;
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=blk_size;
+
+                        /* Decrement number of bytes left this time */
+                        nbytes_toxfer-=blk_size;
+                    } /* end while */
                 } /* end else */
+                break;
 
+            case MPIO:
+                /* Independent file access */
                 if(parms->collective==0) {
-                    mrc = MPI_File_write_at(fd->mpifd, mpi_offset, buffer,
-                                            (int)nelmts_toxfer, ELMT_MPI_TYPE,
-                                            &mpi_status);
-                    VRFY((mrc==MPI_SUCCESS), "MPIO_WRITE");
+                    /* Contiguous pattern */
+                    if (parms->interleaved==0){
+                        /* Compute offset in file */
+                        mpi_offset = mpi_file_offset +
+                            nbytes_xfer;
+
+                        /* Perform independent write */
+                        mrc = MPI_File_write_at(fd->mpifd, mpi_offset, buffer,
+                                    (int)(buf_size/blk_size), mpi_blk_type,
+                                    &mpi_status);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_WRITE");
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=buf_size;
+                    } /* end if */
+                    /* Interleaved access pattern */
+                    else {
+                        /* Set the base of user's buffer */
+                        buf_p=(unsigned char *)buffer;
+
+                        /* Set the number of bytes to transfer this time */
+                        nbytes_toxfer = buf_size;
+
+                        /* Loop over the buffers to write */
+                        while(nbytes_toxfer>0) {
+                            /* Skip offset over blocks of other processes */
+                            mpi_offset = mpi_file_offset +
+                                (nbytes_xfer*pio_mpi_nprocs_g);
+
+                            /* Perform independent write */
+                            mrc = MPI_File_write_at(fd->mpifd, mpi_offset, buf_p,
+                                    (int)1, mpi_blk_type, &mpi_status);
+                            VRFY((mrc==MPI_SUCCESS), "MPIO_WRITE");
+
+                            /* Advance location in buffer */
+                            buf_p+=blk_size;
+
+                            /* Advance global offset in dataset */
+                            nbytes_xfer+=blk_size;
+
+                            /* Decrement number of bytes left this time */
+                            nbytes_toxfer-=blk_size;
+                        } /* end while */
+                    } /* end else */
                 } /* end if */
+                /* Collective file access */
                 else {
-                    mrc = MPI_File_write_at_all(fd->mpifd, mpi_offset, buffer,
-                                            (int)nelmts_toxfer, ELMT_MPI_TYPE,
-                                            &mpi_status);
-                    VRFY((mrc==MPI_SUCCESS), "MPIO_WRITE");
+                    /* Contiguous access pattern */
+                    if (parms->interleaved==0){
+                        /* Compute offset in file */
+                        mpi_offset = mpi_file_offset +
+                            nbytes_xfer;
+
+                        /* Perform independent write */
+                        mrc = MPI_File_write_at_all(fd->mpifd, mpi_offset, buffer,
+                                (int)(buf_size/blk_size), mpi_blk_type, &mpi_status);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_WRITE");
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=buf_size;
+                    } /* end if */
+                    /* Interleaved access pattern */
+                    else {
+                        /* Compute offset in file */
+                        mpi_offset = mpi_file_offset +
+                            (nbytes_xfer*pio_mpi_nprocs_g);
+
+                        /* Set the file view */
+                        mrc = MPI_File_set_view(fd->mpifd, mpi_offset, mpi_blk_type,
+                                mpi_file_type, (char*)"native",  h5_io_info_g);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_VIEW");
+
+                        /* Perform write */
+                        mrc = MPI_File_write_at_all(fd->mpifd, 0, buffer,
+                                (int)(buf_size/blk_size), mpi_blk_type, &mpi_status);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_WRITE");
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=buf_size;
+                    } /* end else */
                 } /* end else */
                 break;
 
             case PHDF5:
-                /* Set up the file dset space id to select the segment to process */
+                /* Set up the file dset space id to move the selection to process */
                 if (parms->interleaved==0){
                     /* Contiguous pattern */
-                    h5start[0] = elmts_begin + nelmts_xfer;
+                    h5offset[0] = nbytes_xfer;
                 } /* end if */
                 else {
                     /* Interleaved access pattern */
                     /* Skip offset over blocks of other processes */
-                    h5start[0] = elmts_begin + (nelmts_xfer*pio_mpi_nprocs_g);
+                    h5offset[0] = (nbytes_xfer*pio_mpi_nprocs_g);
                 } /* end else */
-                h5stride[0] = h5block[0] = nelmts_toxfer;
-                h5count[0] = 1;
-                hrc = H5Sselect_hyperslab(h5dset_space_id, H5S_SELECT_SET,
-                          h5start, h5stride, h5count, h5block); 
-                VRFY((hrc >= 0), "H5Sset_hyperslab");
-
-                /* Only need selection in memory dataset if it is smaller than the whole buffer */
-                if(nelmts_toxfer<nelmts_in_buf) {
-                    /* Setup the memory space id too.  Only start is different */
-                    h5start[0] = 0;
-                    hrc = H5Sselect_hyperslab(h5mem_space_id, H5S_SELECT_SET,
-			      h5start, h5stride, h5count, h5block); 
-                    VRFY((hrc >= 0), "H5Sset_hyperslab");
-                } /* end if */
+                hrc = H5Soffset_simple(h5dset_space_id, h5offset);
+                VRFY((hrc >= 0), "H5Soffset_simple");
 
-                /* set write time here */
+                /* Write the buffer out */
                 hrc = H5Dwrite(h5ds_id, ELMT_H5_TYPE, h5mem_space_id,
                                h5dset_space_id, h5dxpl, buffer);
                 VRFY((hrc >= 0), "H5Dwrite");
+
+                /* Increment number of bytes transferred */
+                nbytes_xfer += buf_size;
+
                 break;
             } /* switch (parms->io_type) */
-
-            /* Increment number of elements transferred */
-            nelmts_xfer += nelmts_toxfer;
-        }
+        } /* end while */
 
         /* Stop "raw data" write timer */
         set_time(res->timers, HDF5_RAW_WRITE_FIXED_DIMS, STOP);
@@ -785,7 +905,7 @@ do_write(results *res, file_descr *fd, parameters *parms, long ndsets,
         /* Calculate write time */
 
         /* Close dataset. Only HDF5 needs to do an explicit close. */
-        if (parms->io_type == PHDF5){
+        if (parms->io_type == PHDF5) {
             hrc = H5Dclose(h5ds_id);
 
             if (hrc < 0) {
@@ -794,10 +914,21 @@ do_write(results *res, file_descr *fd, parameters *parms, long ndsets,
             }
 
             h5ds_id = -1;
-        }
-    }
+        } /* end if */
+    } /* end for */
 
 done:
+    /* release MPI-I/O objects */
+    if (parms->io_type == MPIO) {
+        /* Free file type */
+        mrc = MPI_Type_free( &mpi_file_type );
+        VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_FREE");
+
+        /* Free buffer type */
+        mrc = MPI_Type_free( &mpi_blk_type );
+        VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_FREE");
+    } /* end if */
+
     /* release HDF5 objects */
     if (h5dset_space_id != -1) {
         hrc = H5Sclose(h5dset_space_id);
@@ -841,82 +972,176 @@ done:
  */
 static herr_t
 do_read(results *res, file_descr *fd, parameters *parms, long ndsets,
-        off_t nelmts, size_t buf_size, void *buffer /*out*/)
+         off_t nbytes, size_t buf_size, void *buffer /*out*/)
 {
     int         ret_code = SUCCESS;
     int         rc;             /*routine return code                   */
-    int         mrc;            /*MPI return code                       */
-    MPI_Offset  mpi_offset;
-    MPI_Status  mpi_status;
     long        ndset;
-    off_t       nelmts_xfer;
-    size_t      nelmts_toxfer;
+    size_t      blk_size;       /* The block size to subdivide the xfer buffer into */
+    off_t       nbytes_xfer;    /* Total number of bytes transferred so far */
+    size_t      nbytes_toxfer;  /* Number of bytes to transfer a particular time */
     char        dname[64];
-    off_t       dset_offset=0;    /*dataset offset in a file              */
-    off_t       file_offset;	/*file offset of the next transfer      */
-    off_t       dset_size;      /*one dataset size in bytes             */
-    size_t      nelmts_in_buf;  /*how many element the buffer holds     */
-    off_t       elmts_begin;    /*first elmt this process transfer      */
-    off_t       elmts_count;    /*number of elmts this process transfer */
+    off_t       dset_offset=0;  /*dataset offset in a file              */
+    off_t       bytes_begin;    /*first elmt this process transfer      */
+    off_t       bytes_count;    /*number of elmts this process transfer */
+    unsigned char *buf_p;       /* Current buffer pointer               */
+
+    /* POSIX variables */
+    off_t       file_offset;    /* File offset of the next transfer    */
+    off_t       posix_file_offset;    /* Base file offset of the next transfer      */
+
+    /* MPI variables */
+    MPI_Offset  mpi_file_offset;/* Base file offset of the next transfer*/
+    MPI_Offset	mpi_offset;     /* Offset in MPI file                   */
+    MPI_Datatype mpi_file_type; /* MPI derived type for file            */
+    MPI_Datatype mpi_blk_type;  /* MPI derived type for buffer          */
+    MPI_Status	mpi_status;
+    int         mrc;            /* MPI return code                      */
 
     /* HDF5 variables */
-    herr_t      hrc;            	/*HDF5 return code              */
-    hsize_t     h5dims[1];      	/*dataset dim sizes             */
+    herr_t      hrc;                    /*HDF5 return code              */
+    hsize_t     h5dims[1];              /*dataset dim sizes             */
     hid_t       h5dset_space_id = -1;   /*dataset space ID              */
     hid_t       h5mem_space_id = -1;    /*memory dataspace ID           */
-    hid_t       h5ds_id = -1;   	/*dataset handle                */
-    hsize_t	h5block[1];		/*dataspace selection        */
+    hid_t       h5ds_id = -1;           /*dataset handle                */
+    hsize_t	h5block[1];		/*dataspace selection           */
     hsize_t	h5stride[1];
     hsize_t	h5count[1];
     hssize_t	h5start[1];
+    hssize_t	h5offset[1];            /* Selection offset within dataspace */
     hid_t       h5dxpl = -1;            /* Dataset transfer property list */
 
-    /* calculate dataset parameters. data type is always native C int */
-    dset_size = nelmts * (off_t)ELMT_SIZE;
-    nelmts_in_buf = buf_size/ELMT_SIZE;
-
-    /* hdf5 data space setup */
-    if (parms->io_type == PHDF5){
-        if(nelmts>0) {
-            /* define a contiquous dataset of nelmts native ints */
-            h5dims[0] = nelmts;
-            h5dset_space_id = H5Screate_simple(1, h5dims, NULL);
-            VRFY((h5dset_space_id >= 0), "H5Screate_simple");
-        } /* end if */
-        else {
-            h5dset_space_id = H5Screate(H5S_SCALAR);
-            VRFY((h5dset_space_id >= 0), "H5Screate");
-        } /* end else */
-
-        /* Create the memory dataspace that corresponds to the xfer buffer */
-        if(nelmts_in_buf>0) {
-            h5dims[0] = nelmts_in_buf;
-            h5mem_space_id = H5Screate_simple(1, h5dims, NULL);
-            VRFY((h5mem_space_id >= 0), "H5Screate_simple");
-        } /* end if */
-        else {
-            h5mem_space_id = H5Screate(H5S_SCALAR);
-            VRFY((h5mem_space_id >= 0), "H5Screate");
-        } /* end else */
-
-        /* Create the dataset transfer property list */
-        h5dxpl = H5Pcreate(H5P_DATASET_XFER);
-        if (h5dxpl < 0) {
-            fprintf(stderr, "HDF5 Property List Create failed\n");
-            GOTOERROR(FAIL);
-        }
+    /* Get the parameters from the parameter block */
+    blk_size=parms->blk_size;
+
+    /* There are two kinds of transfer patterns, contiguous and interleaved.
+     * Let 0,1,2,...,n be data accessed by process 0,1,2,...,n
+     *     where n is rank of the last process.
+     * In contiguous pattern, data are accessed as
+     *    000...111...222...nnn...
+     * In interleaved pattern, data are accessed as
+     *    012...n012...n...
+     * These are all in the scope of one dataset.
+     */
+    if (parms->interleaved==0) {
+        /* Contiguous Pattern: */
+        bytes_begin = (off_t)(((double)nbytes*pio_mpi_rank_g)/pio_mpi_nprocs_g);
+    } /* end if */
+    else {
+        /* Interleaved Pattern: */
+        bytes_begin = (off_t)(blk_size*pio_mpi_rank_g);
+    } /* end else */
+
+    /* Calculate the total number of bytes (bytes_count) to be
+     * transferred by this process. It may be different for different
+     * transfer pattern due to rounding to integral values.
+     */
+    /*
+     * Calculate the beginning bytes of this process and the next.
+     * bytes_count is the difference between these two beginnings.
+     * This way, it eliminates any rounding errors.
+     * (This is tricky, don't mess with the formula, rounding errors
+     * can easily get introduced) */
+    bytes_count = (off_t)(((double)nbytes*(pio_mpi_rank_g+1)) / pio_mpi_nprocs_g)
+                  - (off_t)(((double)nbytes*pio_mpi_rank_g) / pio_mpi_nprocs_g);
+
+    /* debug */
+    if (pio_debug_level >= 4) {
+        HDprint_rank(output);
+        HDfprintf(output, "Debug(do_read): "
+            "buf_size=%Hd, bytes_begin=%Hd, bytes_count=%Hd\n",
+            (long_long)buf_size, (long_long)bytes_begin,
+            (long_long)bytes_count);
+    }
 
-        /* Change to collective I/O, if asked */
-        if(parms->collective) {
-            hrc = H5Pset_dxpl_mpio(h5dxpl, H5FD_MPIO_COLLECTIVE);
-            if (hrc < 0) {
-                fprintf(stderr, "HDF5 Property List Set failed\n");
+    /* I/O Access specific setup */
+    switch (parms->io_type) {
+        case POSIXIO:
+            /* No extra setup */
+            break;
+
+        case MPIO: /* MPI-I/O setup */
+            /* Build block's derived type */
+            mrc = MPI_Type_contiguous((int)blk_size,
+                    MPI_BYTE, &mpi_blk_type);
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_CREATE");
+
+            /* Build file's derived type */
+            mrc = MPI_Type_vector((int)(buf_size/blk_size), (int)1,
+                    (int)pio_mpi_nprocs_g, mpi_blk_type, &mpi_file_type);
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_CREATE");
+
+            /* Commit file type */
+            mrc = MPI_Type_commit( &mpi_file_type );
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_COMMIT");
+
+            /* Commit buffer type */
+            mrc = MPI_Type_commit( &mpi_blk_type );
+            VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_COMMIT");
+            break;
+
+        case PHDF5: /* HDF5 setup */
+            if(nbytes>0) {
+                /* define a contiquous dataset of nbytes native bytes */
+                h5dims[0] = nbytes;
+                h5dset_space_id = H5Screate_simple(1, h5dims, NULL);
+                VRFY((h5dset_space_id >= 0), "H5Screate_simple");
+
+                /* Set up the file dset space id to select the pattern to access */
+                if (parms->interleaved==0){
+                    /* Contiguous pattern */
+                    h5start[0] = bytes_begin;
+                    h5stride[0] = h5block[0] = blk_size;
+                    h5count[0] = buf_size/blk_size;
+                } /* end if */
+                else {
+                    /* Interleaved access pattern */
+                    /* Skip offset over blocks of other processes */
+                    h5start[0] = bytes_begin;
+                    h5stride[0] = blk_size*pio_mpi_nprocs_g;
+                    h5block[0] = blk_size;
+                    h5count[0] = buf_size/blk_size;
+                } /* end else */
+                hrc = H5Sselect_hyperslab(h5dset_space_id, H5S_SELECT_SET,
+                          h5start, h5stride, h5count, h5block); 
+                VRFY((hrc >= 0), "H5Sselect_hyperslab");
+            } /* end if */
+            else {
+                h5dset_space_id = H5Screate(H5S_SCALAR);
+                VRFY((h5dset_space_id >= 0), "H5Screate");
+            } /* end else */
+
+            /* Create the memory dataspace that corresponds to the xfer buffer */
+            if(buf_size>0) {
+                h5dims[0] = buf_size;
+                h5mem_space_id = H5Screate_simple(1, h5dims, NULL);
+                VRFY((h5mem_space_id >= 0), "H5Screate_simple");
+            } /* end if */
+            else {
+                h5mem_space_id = H5Screate(H5S_SCALAR);
+                VRFY((h5mem_space_id >= 0), "H5Screate");
+            } /* end else */
+
+            /* Create the dataset transfer property list */
+            h5dxpl = H5Pcreate(H5P_DATASET_XFER);
+            if (h5dxpl < 0) {
+                fprintf(stderr, "HDF5 Property List Create failed\n");
                 GOTOERROR(FAIL);
+            }
+
+            /* Change to collective I/O, if asked */
+            if(parms->collective) {
+                hrc = H5Pset_dxpl_mpio(h5dxpl, H5FD_MPIO_COLLECTIVE);
+                if (hrc < 0) {
+                    fprintf(stderr, "HDF5 Property List Set failed\n");
+                    GOTOERROR(FAIL);
+                } /* end if */
             } /* end if */
-        } /* end if */
-    } /* end if */
+            break;
+    } /* end switch */
 
     for (ndset = 1; ndset <= ndsets; ++ndset) {
+
         /* Calculate dataset offset within a file */
 
         /* create dataset */
@@ -924,7 +1149,7 @@ do_read(results *res, file_descr *fd, parameters *parms, long ndsets,
         case POSIXIO:
         case MPIO:
             /* both posix and mpi io just need dataset offset in file*/
-            dset_offset = (ndset - 1) * dset_size;
+            dset_offset = (ndset - 1) * nbytes;
             break;
 
         case PHDF5:
@@ -938,219 +1163,219 @@ do_read(results *res, file_descr *fd, parameters *parms, long ndsets,
             break;
         }
 
-	/* There are two kinds of transfer patterns, contiguous and interleaved.
-	 * Let 0,1,2,...,n be data accessed by process 0,1,2,...,n
-	 *     where n is rank of the last process.
-	 * In contiguous pattern, data are accessed as
-	 *    000...111...222...nnn...
-	 * In interleaved pattern, data are accessed as
-	 *    012...n012...n...
-	 * These are all in the scope of one dataset.
-	 */
-	/* Calculate the total number of elements (elmts_count) to be
-	 * transferred by this process. It may be different for different
-	 * transfer pattern due to rounding to integral values.
-	 */
-	if (parms->interleaved==0){
-	    /* Contiguous Pattern:
-	     * Calculate the beginning element of this process and the next.
-	     * elmts_count is the difference between these two beginnings.
-	     * This way, it eliminates any rounding errors.
-	     */
-	    elmts_begin = (off_t)(((double)nelmts)/pio_mpi_nprocs_g*pio_mpi_rank_g);
-
-	    /* Do not cast elmt_begin to other types, especially non-integral
-	     * types, else it may introduce rounding discrepency. */
-	    if (pio_mpi_rank_g < (pio_mpi_nprocs_g - 1))
-		elmts_count = (off_t)(((double)nelmts) / pio_mpi_nprocs_g * (pio_mpi_rank_g + 1))
-				- elmts_begin;
-	    else
-		/* last process.  Take whatever are left */
-		elmts_count = nelmts - elmts_begin;
-	} /* end if */
-        else {
-	    /* Interleaved Pattern:
-	     * Each process takes buf_size of elements, starting with the first
-	     * process.  So, the last process may have fewer or even none.
-	     * Calculate the beginning element of this process.
-	     * The elmnts_begin here marks only the beginning of the first
-	     * block accessed by this process.
-	     */
-	    /* Algorithm:
-	     * First allocate equal blocks per process, i.e. one block each
-	     * process for every block_size*nprocs.
-	     * If there is remaining unallocated, give a block each to process
-	     * starting at proc 0.  The last process may get a partial block.
-	     */ 
-	    off_t remain_nelmts, remain_begin;	/* unallocated remaining*/
-
-	    elmts_begin = (off_t)(nelmts_in_buf*pio_mpi_rank_g);
-
-	    /* must use integer calculation next */
-	    /* allocate equal blocks per process */
-	    elmts_count = (nelmts / (off_t)(nelmts_in_buf*pio_mpi_nprocs_g)) *
-			    (off_t)nelmts_in_buf;
-	    remain_nelmts = nelmts % ((off_t)(nelmts_in_buf*pio_mpi_nprocs_g));
-
-	    /* allocate any remaining */
-	    remain_begin = (off_t)(nelmts_in_buf*pio_mpi_rank_g);
-	    if (remain_nelmts > remain_begin) {
-		/* it gets something */
-		if (remain_nelmts > (remain_begin+(off_t)nelmts_in_buf)) {
-		    /* one full block */
-		    elmts_count += nelmts_in_buf;
-		} /* end if */
-                else {
-		    /* only a partial block */
-		    elmts_count += remain_nelmts - remain_begin;
-		} /* end else */
-	    } /* end if */
-	} /* end else */
-	/* debug */
-	if (pio_debug_level >= 4) {
-	    HDprint_rank(output);
-	    HDfprintf(output, "Debug(do_read): "
-		"nelmts_in_buf=%Hd, elmts_begin=%Hd, elmts_count=%Hd\n",
-		(long_long)nelmts_in_buf, (long_long)elmts_begin,
-		(long_long)elmts_count);
-	}
-
-
-	/* The task is to transfer elmts_count elements, starting at
-	 * elmts_begin position, using transfer buffer of buf_size bytes.
+	/* The task is to transfer bytes_count bytes, starting at
+	 * bytes_begin position, using transfer buffer of buf_size bytes.
 	 * If interleaved, select buf_size at a time, in round robin
 	 * fashion, according to number of process. Otherwise, select
-	 * all elmt_count in contiguous.
+	 * all bytes_count in contiguous.
 	 */
-        nelmts_xfer = 0 ;
+        nbytes_xfer = 0 ;
+
+        /* Set base file offset for all I/O patterns and POSIX access */
+        posix_file_offset = dset_offset + bytes_begin;
+
+        /* Set base file offset for all I/O patterns and MPI access */
+        mpi_file_offset = (MPI_Offset)(dset_offset + bytes_begin);
 
         /* Start "raw data" read timer */
         set_time(res->timers, HDF5_RAW_READ_FIXED_DIMS, START);
 
-        while (nelmts_xfer < elmts_count){
-	    /* transfer one buffer of data each round */
-	    /* Note: because size_t is unsigned, avoid expressions that */
-	    /* can be negative. */
-            if ((nelmts_xfer + (off_t)nelmts_in_buf) <= elmts_count) {
-                nelmts_toxfer = nelmts_in_buf;
-            } else {
-                /* last transfer of a partial buffer */
-                nelmts_toxfer = elmts_count - nelmts_xfer;
-            }
-
-            /* read */
+        while (nbytes_xfer < bytes_count){
+            /* Read */
             /* Calculate offset of read within a dataset/file */
-            switch (parms->io_type){
+            switch (parms->io_type) {
             case POSIXIO:
-		if (parms->interleaved==0){
-		    /* Contiguous pattern */
-		    /* need to (off_t) the elmnts_begin expression because they */
-		    /* may be of smaller sized integer types */
-		    file_offset = dset_offset + (off_t)(elmts_begin + nelmts_xfer)*(off_t)ELMT_SIZE;
-		} /* end if */
-                else {
-		    /* Interleaved access pattern */
-                    /* Skip offset over blocks of other processes */
-                    file_offset = dset_offset +
-                        (off_t)(elmts_begin + (nelmts_xfer*pio_mpi_nprocs_g))*(off_t)ELMT_SIZE;
-		} /* end else */
-
-                /* only care if seek returns error */
-                rc = POSIXSEEK(fd->posixfd, file_offset) < 0 ? -1 : 0;
-                VRFY((rc==0), "POSIXSEEK");
-                /* check if all bytes are transferred */
-                rc = ((ssize_t)(nelmts_toxfer*ELMT_SIZE) ==
-                    POSIXREAD(fd->posixfd, buffer, nelmts_toxfer*ELMT_SIZE));
-                VRFY((rc != 0), "POSIXREAD");
-                break;
-
-            case MPIO:
-		if (parms->interleaved==0){
-		    /* Contiguous pattern */
-                    mpi_offset = dset_offset + (elmts_begin + nelmts_xfer)*(off_t)ELMT_SIZE;
+                /* Contiguous pattern */
+                if (parms->interleaved==0) {
+                    /* Compute file offset */
+                    file_offset = posix_file_offset + (off_t)nbytes_xfer;
+
+                    /* only care if seek returns error */
+                    rc = POSIXSEEK(fd->posixfd, file_offset) < 0 ? -1 : 0;
+                    VRFY((rc==0), "POSIXSEEK");
+
+                    /* check if all bytes are written */
+                    rc = ((ssize_t)buf_size ==
+                        POSIXREAD(fd->posixfd, buffer, buf_size));
+                    VRFY((rc != 0), "POSIXREAD");
+
+                    /* Advance global offset in dataset */
+                    nbytes_xfer+=buf_size;
                 } /* end if */
+                /* Interleaved access pattern */
                 else {
-		    /* Interleaved access pattern */
-                    /* Skip offset over blocks of other processes */
-                    mpi_offset = dset_offset + (elmts_begin + (nelmts_xfer*pio_mpi_nprocs_g))*(off_t)ELMT_SIZE;
+                    /* Set the base of user's buffer */
+                    buf_p=(unsigned char *)buffer;
+
+                    /* Set the number of bytes to transfer this time */
+                    nbytes_toxfer = buf_size;
+
+                    /* Loop over the buffers to read */
+                    while(nbytes_toxfer>0) {
+                        /* Skip offset over blocks of other processes */
+                        file_offset = posix_file_offset +
+                            (off_t)(nbytes_xfer*pio_mpi_nprocs_g);
+
+                        /* only care if seek returns error */
+                        rc = POSIXSEEK(fd->posixfd, file_offset) < 0 ? -1 : 0;
+                        VRFY((rc==0), "POSIXSEEK");
+
+                        /* check if all bytes are written */
+                        rc = ((ssize_t)blk_size ==
+                            POSIXREAD(fd->posixfd, buf_p, blk_size));
+                        VRFY((rc != 0), "POSIXREAD");
+
+                        /* Advance location in buffer */
+                        buf_p+=blk_size;
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=blk_size;
+
+                        /* Decrement number of bytes left this time */
+                        nbytes_toxfer-=blk_size;
+                    } /* end while */
                 } /* end else */
+                break;
 
+            case MPIO:
+                /* Independent file access */
                 if(parms->collective==0) {
-                    mrc = MPI_File_read_at(fd->mpifd, mpi_offset, buffer,
-                                           (int)nelmts_toxfer, ELMT_MPI_TYPE,
-                                           &mpi_status);
-                    VRFY((mrc==MPI_SUCCESS), "MPIO_read");
+                    /* Contiguous pattern */
+                    if (parms->interleaved==0){
+                        /* Compute offset in file */
+                        mpi_offset = mpi_file_offset +
+                            nbytes_xfer;
+
+                        /* Perform independent read */
+                        mrc = MPI_File_read_at(fd->mpifd, mpi_offset, buffer,
+                                    (int)(buf_size/blk_size), mpi_blk_type,
+                                    &mpi_status);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_READ");
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=buf_size;
+                    } /* end if */
+                    /* Interleaved access pattern */
+                    else {
+                        /* Set the base of user's buffer */
+                        buf_p=(unsigned char *)buffer;
+
+                        /* Set the number of bytes to transfer this time */
+                        nbytes_toxfer = buf_size;
+
+                        /* Loop over the buffers to read */
+                        while(nbytes_toxfer>0) {
+                            /* Skip offset over blocks of other processes */
+                            mpi_offset = mpi_file_offset +
+                                (nbytes_xfer*pio_mpi_nprocs_g);
+
+                            /* Perform independent read */
+                            mrc = MPI_File_read_at(fd->mpifd, mpi_offset, buf_p,
+                                    (int)1, mpi_blk_type, &mpi_status);
+                            VRFY((mrc==MPI_SUCCESS), "MPIO_READ");
+
+                            /* Advance location in buffer */
+                            buf_p+=blk_size;
+
+                            /* Advance global offset in dataset */
+                            nbytes_xfer+=blk_size;
+
+                            /* Decrement number of bytes left this time */
+                            nbytes_toxfer-=blk_size;
+                        } /* end while */
+                    } /* end else */
                 } /* end if */
+                /* Collective file access */
                 else {
-                    mrc = MPI_File_read_at_all(fd->mpifd, mpi_offset, buffer,
-                                           (int)nelmts_toxfer, ELMT_MPI_TYPE,
-                                           &mpi_status);
-                    VRFY((mrc==MPI_SUCCESS), "MPIO_read");
+                    /* Contiguous access pattern */
+                    if (parms->interleaved==0){
+                        /* Compute offset in file */
+                        mpi_offset = mpi_file_offset +
+                            nbytes_xfer;
+
+                        /* Perform collective read */
+                        mrc = MPI_File_read_at_all(fd->mpifd, mpi_offset, buffer,
+                                (int)(buf_size/blk_size), mpi_blk_type, &mpi_status);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_READ");
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=buf_size;
+                    } /* end if */
+                    /* Interleaved access pattern */
+                    else {
+                        /* Compute offset in file */
+                        mpi_offset = mpi_file_offset +
+                            (nbytes_xfer*pio_mpi_nprocs_g);
+
+                        /* Set the file view */
+                        mrc = MPI_File_set_view(fd->mpifd, mpi_offset, mpi_blk_type,
+                                mpi_file_type, (char*)"native",  h5_io_info_g);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_VIEW");
+
+                        /* Perform collective read */
+                        mrc = MPI_File_read_at_all(fd->mpifd, 0, buffer,
+                                (int)(buf_size/blk_size), mpi_blk_type, &mpi_status);
+                        VRFY((mrc==MPI_SUCCESS), "MPIO_READ");
+
+                        /* Advance global offset in dataset */
+                        nbytes_xfer+=buf_size;
+                    } /* end else */
                 } /* end else */
                 break;
 
             case PHDF5:
-                /* Set up the dset space id to select the segment to process */
+                /* Set up the file dset space id to move the selection to process */
                 if (parms->interleaved==0){
                     /* Contiguous pattern */
-                    h5start[0] = elmts_begin + nelmts_xfer;
+                    h5offset[0] = nbytes_xfer;
                 } /* end if */
                 else {
                     /* Interleaved access pattern */
                     /* Skip offset over blocks of other processes */
-                    h5start[0] = elmts_begin + (nelmts_xfer*pio_mpi_nprocs_g);
+                    h5offset[0] = (nbytes_xfer*pio_mpi_nprocs_g);
                 } /* end else */
-                h5stride[0] = h5block[0] = nelmts_toxfer;
-                h5count[0] = 1;
-                hrc = H5Sselect_hyperslab(h5dset_space_id, H5S_SELECT_SET,
-                          h5start, h5stride, h5count, h5block); 
-                VRFY((hrc >= 0), "H5Sset_hyperslab");
-
-                /* Only need selection in memory dataset if it is smaller than the whole buffer */
-                if(nelmts_toxfer<nelmts_in_buf) {
-                    /* Setup the memory space id too.  Only start is different */
-                    h5start[0] = 0;
-                    hrc = H5Sselect_hyperslab(h5mem_space_id, H5S_SELECT_SET,
-			      h5start, h5stride, h5count, h5block); 
-                    VRFY((hrc >= 0), "H5Sset_hyperslab");
-                } /* end if */
+                hrc = H5Soffset_simple(h5dset_space_id, h5offset);
+                VRFY((hrc >= 0), "H5Soffset_simple");
 
-                /* set read time here */
+                /* Read the buffer in */
                 hrc = H5Dread(h5ds_id, ELMT_H5_TYPE, h5mem_space_id,
-                              h5dset_space_id, h5dxpl, buffer);
+                               h5dset_space_id, h5dxpl, buffer);
                 VRFY((hrc >= 0), "H5Dread");
+
+                /* Increment number of bytes transferred */
+                nbytes_xfer += buf_size;
+
                 break;
             } /* switch (parms->io_type) */
 
+            /* Verify raw data, if asked */
 	    if (parms->verify) {
-		/*verify read data*/
-                int *intptr = (int *)buffer;
+		/* Verify data read */
+                unsigned char *ucharptr = (unsigned char *)buffer;
                 size_t i;
 		int nerror=0;
 
-                for (i = 0; i < nelmts_toxfer; ++i){
-                    if (*intptr++ != pio_mpi_rank_g){
+                for (i = 0; i < buf_size; ++i){
+                    if (*ucharptr++ != pio_mpi_rank_g) {
 			if (++nerror < 20){
 			    /* report at most 20 errors */
 			    HDprint_rank(output);
 			    HDfprintf(output, "read data error, expected (%Hd), "
 				     "got (%Hd)\n",
 				     (long_long)pio_mpi_rank_g,
-				     (long_long)*(intptr-1));
-			}
-		    }
-		}
+				     (long_long)*(ucharptr-1));
+			} /* end if */
+		    } /* end if */
+		} /* end for */
 		if (nerror >= 20) {
 		    HDprint_rank(output);
 		    HDfprintf(output, "...");
-		    HDfprintf(output, "total read data errors=%Hd\n",
+		    HDfprintf(output, "total read data errors=%d\n",
 			    nerror);
-		}
+		} /* end if */
             }	/* if (parms->verify) */
 
-            /* Increment number of elements transferred */
-            nelmts_xfer += nelmts_toxfer;
-        }
+        } /* end while */
 
         /* Stop "raw data" read timer */
         set_time(res->timers, HDF5_RAW_READ_FIXED_DIMS, STOP);
@@ -1158,7 +1383,7 @@ do_read(results *res, file_descr *fd, parameters *parms, long ndsets,
         /* Calculate read time */
 
         /* Close dataset. Only HDF5 needs to do an explicit close. */
-        if (parms->io_type == PHDF5){
+        if (parms->io_type == PHDF5) {
             hrc = H5Dclose(h5ds_id);
 
             if (hrc < 0) {
@@ -1167,10 +1392,21 @@ do_read(results *res, file_descr *fd, parameters *parms, long ndsets,
             }
 
             h5ds_id = -1;
-        }
-    }
+        } /* end if */
+    } /* end for */
 
 done:
+    /* release MPI-I/O objects */
+    if (parms->io_type == MPIO) {
+        /* Free file type */
+        mrc = MPI_Type_free( &mpi_file_type );
+        VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_FREE");
+
+        /* Free buffer type */
+        mrc = MPI_Type_free( &mpi_blk_type );
+        VRFY((mrc==MPI_SUCCESS), "MPIO_TYPE_FREE");
+    } /* end if */
+
     /* release HDF5 objects */
     if (h5dset_space_id != -1) {
         hrc = H5Sclose(h5dset_space_id);
@@ -1713,6 +1949,8 @@ invalidate_file_cache(const char *filename)
 
 #else
 
+/* turn the stubs off since some compilers are warning they are not used */
+#if 0
 /* H5_HAVE_GPFS isn't defined...stub functions */
 
 static void
@@ -1757,6 +1995,8 @@ invalidate_file_cache(const char UNUSED *filename)
     return;
 }
 
+#endif  /* 0 */
+
 #endif  /* H5_HAVE_GPFS */
 
 #ifdef TIME_MPI
diff --git a/perform/pio_perf.c b/perform/pio_perf.c
index 0f43f15..5ddac67 100644
--- a/perform/pio_perf.c
+++ b/perform/pio_perf.c
@@ -109,7 +109,7 @@ int         pio_debug_level = 0;/* The debug level:
                                  */
 
 /* local variables */
-static const char  *progname = "pio_perf";
+static const char  *progname = "h5perf";
 
 /*
  * Command-line options: The user can specify short or long-named
@@ -117,14 +117,11 @@ static const char  *progname = "pio_perf";
  * adding more, make sure that they don't clash with each other.
  */
 #if 1
-static const char *s_opts = "ha:A:cCD:f:P:p:X:x:nd:F:i:Io:stT:w";
+static const char *s_opts = "a:A:B:cCd:D:e:F:hi:Ino:p:P:stT:wx:X:";
 #else
-static const char *s_opts = "ha:A:bcCD:f:P:p:X:x:nd:F:i:Io:stT:w";
+static const char *s_opts = "a:A:bB:cCd:D:e:F:hi:Ino:p:P:stT:wx:X:";
 #endif  /* 1 */
 static struct long_options l_opts[] = {
-    { "help", no_arg, 'h' },
-    { "hel", no_arg, 'h' },
-    { "he", no_arg, 'h' },
     { "align", require_arg, 'a' },
     { "alig", require_arg, 'a' },
     { "ali", require_arg, 'a' },
@@ -139,6 +136,15 @@ static struct long_options l_opts[] = {
     { "bin", no_arg, 'b' },
     { "bi", no_arg, 'b' },
 #endif  /* 0 */
+    { "block-size", require_arg, 'B' },
+    { "block-siz", require_arg, 'B' },
+    { "block-si", require_arg, 'B' },
+    { "block-s", require_arg, 'B' },
+    { "block-", require_arg, 'B' },
+    { "block", require_arg, 'B' },
+    { "bloc", require_arg, 'B' },
+    { "blo", require_arg, 'B' },
+    { "bl", require_arg, 'B' },
     { "chunk", no_arg, 'c' },
     { "chun", no_arg, 'c' },
     { "chu", no_arg, 'c' },
@@ -156,13 +162,9 @@ static struct long_options l_opts[] = {
     { "debu", require_arg, 'D' },
     { "deb", require_arg, 'D' },
     { "de", require_arg, 'D' },
-    { "file-size", require_arg, 'f' },
-    { "file-siz", require_arg, 'f' },
-    { "file-si", require_arg, 'f' },
-    { "file-s", require_arg, 'f' },
-    { "file", require_arg, 'f' },
-    { "fil", require_arg, 'f' },
-    { "fi", require_arg, 'f' },
+    { "help", no_arg, 'h' },
+    { "hel", no_arg, 'h' },
+    { "he", no_arg, 'h' },
     { "interleaved", require_arg, 'I' },
     { "interleave", require_arg, 'I' },
     { "interleav", require_arg, 'I' },
@@ -213,6 +215,11 @@ static struct long_options l_opts[] = {
     { "no-f", no_arg, 'n' },
     { "no-", no_arg, 'n' },
     { "no", no_arg, 'n' },
+    { "num-bytes", require_arg, 'e' },
+    { "num-byte", require_arg, 'e' },
+    { "num-byt", require_arg, 'e' },
+    { "num-by", require_arg, 'e' },
+    { "num-b", require_arg, 'e' },
     { "num-dsets", require_arg, 'd' },
     { "num-dset", require_arg, 'd' },
     { "num-dse", require_arg, 'd' },
@@ -260,14 +267,15 @@ static struct long_options l_opts[] = {
 struct options {
     long io_types;              /* bitmask of which I/O types to test   */
     const char *output_file;    /* file to print report to              */
-    off_t file_size;            /* size of file                         */
     long num_dsets;             /* number of datasets                   */
     long num_files;             /* number of files                      */
+    size_t num_bpp;             /* number of bytes per proc per dset    */
     int num_iters;              /* number of iterations                 */
     int max_num_procs;          /* maximum number of processes to use   */
     int min_num_procs;          /* minimum number of processes to use   */
     size_t max_xfer_size;       /* maximum transfer buffer size         */
     size_t min_xfer_size;       /* minimum transfer buffer size         */
+    size_t blk_size;            /* Block size                           */
     unsigned interleaved;       /* Interleaved vs. contiguous blocks    */
     unsigned collective;        /* Collective vs. independent I/O       */
     int print_times;       	/* print times as well as throughputs   */
@@ -410,6 +418,7 @@ run_test_loop(struct options *opts)
     parms.num_files = opts->num_files;
     parms.num_dsets = opts->num_dsets;
     parms.num_iters = opts->num_iters;
+    parms.blk_size = opts->blk_size;
     parms.interleaved = opts->interleaved;
     parms.collective = opts->collective;
     parms.h5_align = opts->h5_alignment;
@@ -439,17 +448,16 @@ run_test_loop(struct options *opts)
             for (buf_size = opts->min_xfer_size;
                     buf_size <= opts->max_xfer_size; buf_size <<= 1) {
                 parms.buf_size = buf_size;
-                parms.num_elmts = opts->file_size /
-                                    (off_t)(parms.num_dsets * sizeof(int));
+                parms.num_bytes = (off_t)opts->num_bpp*parms.num_procs;
 
                 print_indent(1);
                 output_report("Transfer Buffer Size: %ld bytes, File size: %.2f MBs\n",
                               buf_size,
-                              ((double)parms.num_dsets * (double)parms.num_elmts *
-                                    (double)sizeof(int)) / ONE_MB);
+                              ((double)parms.num_dsets * (double)parms.num_bytes)
+                                / ONE_MB);
                 print_indent(1);
-                output_report("  # of files: %ld, # of dsets: %ld, # of elmts per dset: %ld\n",
-                              parms.num_files, parms.num_dsets, parms.num_elmts);
+                output_report("  # of files: %ld, # of datasets: %ld, dataset size: %.2f MBs\n",
+                              parms.num_files, parms.num_dsets, (double)parms.num_bytes/ONE_MB);
 
                 if (opts->io_types & PIO_POSIX)
                     run_test(POSIXIO, parms, opts);
@@ -503,7 +511,7 @@ run_test(iotype iot, parameters parms, struct options *opts)
     minmax          read_gross_mm = {0.0, 0.0, 0.0, 0};
     minmax          read_raw_mm = {0.0, 0.0, 0.0, 0};
 
-    raw_size = (off_t)parms.num_dsets * (off_t)parms.num_elmts * (off_t)sizeof(int);
+    raw_size = (off_t)parms.num_dsets * (off_t)parms.num_bytes;
     parms.io_type = iot;
     print_indent(2);
     output_report("IO API = ");
@@ -996,8 +1004,8 @@ report_parameters(struct options *opts)
     HDfprintf(output, "rank %d: IO API=", rank);
     print_io_api(opts->io_types);
 
-    HDfprintf(output, "rank %d: File size=", rank);
-    recover_size_and_print((long_long)opts->file_size, "\n");
+    HDfprintf(output, "rank %d: Number of bytes per process per dataset=", rank);
+    recover_size_and_print((long_long)opts->num_bpp, "\n");
 
     HDfprintf(output, "rank %d: Number of files=%Hd\n", rank,
               (long_long)opts->num_files);
@@ -1008,9 +1016,21 @@ report_parameters(struct options *opts)
     HDfprintf(output, "rank %d: Number of processes=%d:%d\n", rank,
               opts->min_num_procs, opts->max_num_procs);
 
+    HDfprintf(output, "rank %d: Size of dataset(s)=", rank);
+    recover_size_and_print((long_long)(opts->num_bpp * opts->min_num_procs), ":");
+    recover_size_and_print((long_long)(opts->num_bpp * opts->max_num_procs), "\n");
+
+    HDfprintf(output, "rank %d: File size=", rank);
+    recover_size_and_print((long_long)(opts->num_bpp * opts->min_num_procs
+                                            * opts->num_dsets), ":");
+    recover_size_and_print((long_long)(opts->num_bpp * opts->max_num_procs
+                                            * opts->num_dsets), "\n");
+
     HDfprintf(output, "rank %d: Transfer buffer size=", rank);
     recover_size_and_print((long_long)opts->min_xfer_size, ":");
     recover_size_and_print((long_long)opts->max_xfer_size, "\n");
+    HDfprintf(output, "rank %d: Block size=", rank);
+    recover_size_and_print((long_long)opts->blk_size, "\n");
 
     HDfprintf(output, "rank %d: Block Pattern in Dataset=", rank);
     if(opts->interleaved)
@@ -1055,15 +1075,16 @@ parse_command_line(int argc, char *argv[])
     cl_opts = (struct options *)malloc(sizeof(struct options));
 
     cl_opts->output_file = NULL;
-    cl_opts->file_size = 64 * ONE_MB;
     cl_opts->io_types =  0;    /* will set default after parsing options */
     cl_opts->num_dsets = 1;
     cl_opts->num_files = 1;
+    cl_opts->num_bpp = 256 * ONE_KB;
     cl_opts->num_iters = 1;
     cl_opts->max_num_procs = comm_world_nprocs_g;
     cl_opts->min_num_procs = 1;
     cl_opts->max_xfer_size = 1 * ONE_MB;
     cl_opts->min_xfer_size = 128 * ONE_KB;
+    cl_opts->blk_size = 128 * ONE_KB;   /* Default to writing 128K per block */
     cl_opts->interleaved = 0;       /* Default to contiguous blocks in dataset */
     cl_opts->collective = 0;        /* Default to independent I/O access */
     cl_opts->print_times = FALSE;   /* Printing times is off by default */
@@ -1119,6 +1140,9 @@ parse_command_line(int argc, char *argv[])
             /* the future "binary" option */
             break;
 #endif  /* 0 */
+        case 'B':
+            cl_opts->blk_size = parse_size_directive(opt_arg);
+            break;
         case 'c':
             /* Turn on chunked HDF5 dataset creation */
             cl_opts->h5_use_chunks = TRUE;
@@ -1187,8 +1211,8 @@ parse_command_line(int argc, char *argv[])
             }
 
             break;
-        case 'f':
-            cl_opts->file_size = parse_size_directive(opt_arg);
+        case 'e':
+            cl_opts->num_bpp = parse_size_directive(opt_arg);
             break;
         case 'F':
             cl_opts->num_files = atoi(opt_arg);
@@ -1318,15 +1342,20 @@ usage(const char *prog)
 #if 0
         printf("     -b, --binary                The elusive binary option\n");
 #endif  /* 0 */
+        printf("     -B S, --block-size=S        Block size within transfer buffer\n");
+        printf("                                 (see below for description)\n");
+        printf("                                 [default:128K]\n");
         printf("     -c, --chunk                 Create HDF5 datasets chunked [default: off]\n");
-        printf("     -C, --collective            Use collective I/O for MPI and HDF5 APIs [default: off (i.e. independent I/O)]\n");
+        printf("     -C, --collective            Use collective I/O for MPI and HDF5 APIs\n");
+        printf("                                 [default: off (i.e. independent I/O)]\n");
         printf("     -d N, --num-dsets=N         Number of datasets per file [default:1]\n");
         printf("     -D DL, --debug=DL           Indicate the debugging level\n");
         printf("                                 [default: no debugging]\n");
-        printf("     -f S, --file-size=S         Size of a single file [default: 64M]\n");
+        printf("     -e S, --num-bytes=S         Number of bytes per process per dataset\n");
+        printf("                                 [default: 256K]\n");
         printf("     -F N, --num-files=N         Number of files [default: 1]\n");
         printf("     -i, --num-iterations        Number of iterations to perform [default: 1]\n");
-        printf("     -I --interleaved            Interleaved block I/O (see below for example)\n");
+        printf("     -I, --interleaved           Interleaved block I/O (see below for example)\n");
         printf("                                 [default: Contiguous block I/O]\n");
         printf("     -n, --no-fill               Don't write fill values to HDF5 dataset\n");
         printf("                                 (Supported in HDF5 library v1.5 only)\n");
@@ -1348,7 +1377,7 @@ usage(const char *prog)
         printf("          M - Megabyte (%d)\n", ONE_MB);
         printf("          G - Gigabyte (%d)\n", ONE_GB);
         printf("\n");
-        printf("      Example: 37M = 37 Megabytes = %d bytes\n", 37*ONE_MB);
+        printf("      Example: '37M' is 37 megabytes or %d bytes\n", 37*ONE_MB);
         printf("\n");
         printf("  AL - is an API list. Valid values are:\n");
         printf("          phdf5 - Parallel HDF5\n");
@@ -1357,24 +1386,50 @@ usage(const char *prog)
         printf("\n");
         printf("      Example: --api=mpiio,phdf5\n");
         printf("\n");
+        printf("  Block size vs. Transfer buffer size:\n");
+        printf("      The transfer buffer size is the size of a buffer in memory, which is\n");
+        printf("      broken into 'block size' pieces and written to the file.  The pattern\n");
+        printf("      of the blocks in the file is described below in the 'Interleaved vs.\n");
+        printf("      Contiguous blocks' example.\n");
+        printf("\n");
+        printf("      If the collective I/O option is given, the blocks in each transfer buffer\n");
+        printf("      are written at once with an MPI derived type, for the MPI-I/O and PHDF5\n");
+        printf("      APIs.\n");
+        printf("\n");
         printf("  Interleaved vs. Contiguous blocks:\n");
-        printf("      For example, with a 4 process run,\n");
-        printf("          Contiguous blocks are written to the file like so:\n");
-        printf("              1111222233334444\n");
-        printf("          Interleaved blocks are written to the file like so:\n");
-        printf("              1234123412341234\n");
+        printf("      When contiguous blocks are written to a dataset, the dataset is divided\n");
+        printf("      into '# processes' regions and each process writes data to its own region.\n");
+        printf("      When interleaved blocks are written to a dataset, space for the first\n");
+        printf("      block of the first process is allocated in the dataset, then space is\n");
+        printf("      allocated for the first block of the second process, etc. until space is\n");
+        printf("      allocated for the first block of each process, then space is allocated for\n");
+        printf("      the second block of the first process, the second block of the second\n");
+        printf("      process, etc.\n");
+        printf("\n");
+        printf("      For example, with a 4 process run, 1MB bytes-per-process, 256KB transfer\n");
+        printf("        buffer size, and 64KB block size,\n");
+        printf("          16 contiguous blocks per process are written to the file like so:\n");
+        printf("              1111111111111111222222222222222233333333333333334444444444444444\n");
+        printf("          16 interleaved blocks per process are written to the file like so:\n");
+        printf("              1234123412341234123412341234123412341234123412341234123412341234\n");
+        printf("        If collective I/O is turned on, all of the four blocks per transfer\n");
+        printf("        buffer will be written in one collective I/O call.\n");
         printf("\n");
         printf("  DL - is a list of debugging flags. Valid values are:\n");
         printf("          1 - Minimal\n");
         printf("          2 - Not quite everything\n");
         printf("          3 - Everything\n");
-        printf("          4 - Everything and the kitchen sink\n");
+        printf("          4 - The kitchen sink\n");
         printf("          r - Raw data I/O throughput information\n");
         printf("          t - Times as well as throughputs\n");
         printf("          v - Verify data correctness\n");
         printf("\n");
         printf("      Example: --debug=2,r,t\n");
         printf("\n");
+        printf("  Environment variables:\n");
+        printf("  HDF5_NOCLEANUP   Do not remove data files if set [default remove]\n");
+        printf("  HDF5_MPI_INFO    MPI INFO object key=value separated by ;\n");
+        printf("  HDF5_PARAPREFIX  Paralllel data files prefix\n");
         fflush(stdout);
     }
 }
diff --git a/perform/pio_perf.h b/perform/pio_perf.h
index e245e8a..5053eb2 100644
--- a/perform/pio_perf.h
+++ b/perform/pio_perf.h
@@ -36,9 +36,10 @@ typedef struct parameters_ {
     int		num_procs;      /* Maximum number of processes to use   */
     long	num_files;      /* Number of files to create            */
     long	num_dsets;      /* Number of datasets to create         */
-    off_t	num_elmts;      /* Number of native ints in each dset   */
+    off_t	num_bytes;      /* Number of bytes in each dset         */
     int         num_iters;      /* Number of times to loop doing the IO */
     size_t 	buf_size;       /* Buffer size                          */
+    size_t 	blk_size;       /* Block size                           */
     unsigned    interleaved;    /* Interleaved vs. contiguous blocks    */
     unsigned    collective;     /* Collective vs. independent I/O       */
     hsize_t 	h5_align;       /* HDF5 object alignment                */