[svn-r21442] Description:

    Check in "actual I/O mode" feature to trunk.  Will merge back to 1.8 branch
after it bakes over the weekend.

Tested on:
    FreeBSD/32 8.2 (loyalty) w/gcc4.6, w/C++ & FORTRAN, in debug mode
    FreeBSD/64 8.2 (freedom) w/gcc4.6, w/C++ & FORTRAN, in debug mode
    Linux/32 2.6 (jam) w/PGI compilers, w/default API=1.8.x,
        w/C++ & FORTRAN, w/threadsafe, in debug mode
    Linux/64-amd64 2.6 (koala) w/Intel compilers, w/default API=1.6.x,
        w/C++ & FORTRAN, in production mode
    Solaris/32 2.10 (linew) w/deprecated symbols disabled, w/C++ & FORTRAN,
        w/szip filter, w/threadsafe, in production mode
    Linux/PPC 2.6 (heiwa) w/C++ & FORTRAN, w/threadsafe, in debug mode
    Linux/64-ia64 2.6 (ember) w/Intel compilers, w/C++ & FORTRAN,
        in production mode
    Linux/64-amd64 2.6 (abe) w/parallel, w/FORTRAN, in debug mode
    Mac OS X/32 10.6.8 (amazon) in debug mode
    Mac OS X/32 10.6.8 (amazon) w/C++ & FORTRAN, w/threadsafe,
        in production mode

9 files changed, 795 insertions, 16 deletions

diff --git a/src/H5Dio.c b/src/H5Dio.c
index 7ee304c..7268b25 100644
--- a/src/H5Dio.c
+++ b/src/H5Dio.c
@@ -340,7 +340,7 @@ H5D_read(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
 #ifdef H5_HAVE_PARALLEL
     /* Collective access is not permissible without a MPI based VFD */
     if(dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE && 
-      !(H5F_HAS_FEATURE(dataset->oloc.file, H5FD_FEAT_HAS_MPI)))
+            !(H5F_HAS_FEATURE(dataset->oloc.file, H5FD_FEAT_HAS_MPI)))
         HGOTO_ERROR(H5E_DATASET, H5E_UNSUPPORTED, FAIL, "collective access for MPI-based drivers only")
 #endif /*H5_HAVE_PARALLEL*/
 
@@ -603,7 +603,7 @@ H5D_write(H5D_t *dataset, hid_t mem_type_id, const H5S_t *mem_space,
             HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, FAIL, "unable to construct projected memory dataspace")
         HDassert(projected_mem_space);
         HDassert(adj_buf);
-            
+
         /* Switch to using projected memory dataspace & adjusted buffer */
         mem_space = projected_mem_space;
         buf = adj_buf;
@@ -950,6 +950,9 @@ H5D_ioinfo_adjust(H5D_io_info_t *io_info, const H5D_t *dset, hid_t dxpl_id,
     const H5S_t *file_space, const H5S_t *mem_space,
     const H5D_type_info_t *type_info, const H5D_chunk_map_t *fm)
 {
+    H5P_genplist_t *dx_plist;       /* Data transer property list */
+    H5D_mpio_actual_chunk_opt_mode_t actual_chunk_opt_mode; /* performed chunk optimization */
+    H5D_mpio_actual_io_mode_t actual_io_mode; /* performed io mode */
     herr_t	ret_value = SUCCEED;	/* Return value	*/
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_ioinfo_adjust)
@@ -963,6 +966,20 @@ H5D_ioinfo_adjust(H5D_io_info_t *io_info, const H5D_t *dset, hid_t dxpl_id,
     HDassert(type_info->tpath);
     HDassert(io_info);
 
+    /* Get the dataset transfer property list */
+    if(NULL == (dx_plist = (H5P_genplist_t *)H5I_object(dxpl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset transfer property list")
+
+    /* Reset the actual io mode properties to the default values in case
+     * the dxpl was previously used in a collective I/O operation.
+     */
+    actual_chunk_opt_mode = H5D_MPIO_NO_CHUNK_OPTIMIZATION;
+    actual_io_mode = H5D_MPIO_NO_COLLECTIVE;
+    if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME, &actual_chunk_opt_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual chunk opt mode property")
+    if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_IO_MODE_NAME, &actual_io_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual io mode property")
+
     /* Make any parallel I/O adjustments */
     if(io_info->using_mpi_vfd) {
         htri_t opt;         /* Flag whether a selection is optimizable */
@@ -995,12 +1012,6 @@ H5D_ioinfo_adjust(H5D_io_info_t *io_info, const H5D_t *dset, hid_t dxpl_id,
              * mark it so that we remember to revert the change.
              */
             if(io_info->dxpl_cache->xfer_mode == H5FD_MPIO_COLLECTIVE) {
-                H5P_genplist_t *dx_plist;           /* Data transer property list */
-
-                /* Get the dataset transfer property list */
-                if(NULL == (dx_plist = (H5P_genplist_t *)H5I_object(dxpl_id)))
-                    HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataset creation property list")
-
                 /* Change the xfer_mode to independent for handling the I/O */
                 io_info->dxpl_cache->xfer_mode = H5FD_MPIO_INDEPENDENT;
                 if(H5P_set(dx_plist, H5D_XFER_IO_XFER_MODE_NAME, &io_info->dxpl_cache->xfer_mode) < 0)
diff --git a/src/H5Dmpio.c b/src/H5Dmpio.c
index 1c69305..8c78af2 100644
--- a/src/H5Dmpio.c
+++ b/src/H5Dmpio.c
@@ -471,6 +471,8 @@ H5D_contig_collective_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_i
     hsize_t UNUSED nelmts, const H5S_t *file_space, const H5S_t *mem_space,
     H5D_chunk_map_t UNUSED *fm)
 {
+    H5D_mpio_actual_io_mode_t actual_io_mode = H5D_MPIO_CONTIGUOUS_COLLECTIVE;
+    H5P_genplist_t *dx_plist;           /* Pointer to DXPL */
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI(H5D_contig_collective_read, FAIL)
@@ -483,6 +485,16 @@ H5D_contig_collective_read(H5D_io_info_t *io_info, const H5D_type_info_t *type_i
     if(H5D_inter_collective_io(io_info, type_info, file_space, mem_space) < 0)
         HGOTO_ERROR(H5E_IO, H5E_READERROR, FAIL, "couldn't finish shared collective MPI-IO")
 
+    /* Obtain the data transfer properties */
+    if(NULL == (dx_plist = H5I_object(io_info->dxpl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data transfer property list")
+
+    /* Set the actual I/O mode property. internal_collective_io will not break to
+     * independent I/O, so we set it here.
+     */
+    if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_IO_MODE_NAME, &actual_io_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual io mode property")
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_contig_collective_read() */
@@ -506,6 +518,8 @@ H5D_contig_collective_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_
     hsize_t UNUSED nelmts, const H5S_t *file_space, const H5S_t *mem_space,
     H5D_chunk_map_t UNUSED *fm)
 {
+    H5D_mpio_actual_io_mode_t actual_io_mode = H5D_MPIO_CONTIGUOUS_COLLECTIVE;
+    H5P_genplist_t *dx_plist;           /* Pointer to DXPL */
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI(H5D_contig_collective_write, FAIL)
@@ -518,6 +532,16 @@ H5D_contig_collective_write(H5D_io_info_t *io_info, const H5D_type_info_t *type_
     if(H5D_inter_collective_io(io_info, type_info, file_space, mem_space) < 0)
         HGOTO_ERROR(H5E_IO, H5E_WRITEERROR, FAIL, "couldn't finish shared collective MPI-IO")
 
+    /* Obtain the data transfer properties */
+    if(NULL == (dx_plist = H5I_object(io_info->dxpl_id)))
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data transfer property list")
+
+    /* Set the actual I/O mode property. internal_collective_io will not break to
+     * independent I/O, so we set it here.
+     */
+    if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_IO_MODE_NAME, &actual_io_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual io mode property")
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_contig_collective_write() */
@@ -559,6 +583,8 @@ H5D_chunk_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *type_info
 {
     H5P_genplist_t *dx_plist;           /* Pointer to DXPL */
     H5FD_mpio_chunk_opt_t chunk_opt_mode;
+    H5D_mpio_actual_chunk_opt_mode_t actual_chunk_opt_mode;
+    H5D_mpio_actual_io_mode_t actual_io_mode;
     int         io_option = H5D_MULTI_CHUNK_IO_MORE_OPT;
     int         sum_chunk = -1;
 #ifdef H5_HAVE_INSTRUMENTED_LIBRARY
@@ -646,15 +672,38 @@ H5D_chunk_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *type_info
 
     /* step 2:  Go ahead to do IO.*/
     if(io_option == H5D_ONE_LINK_CHUNK_IO || io_option == H5D_ONE_LINK_CHUNK_IO_MORE_OPT) {
+        /* set the actual io mode properties to the correct values for link chunk io.
+         * Link chunk I/O does not break to independent, so we can set the actual_io mode
+         * as well as the optimisation mode. */
+        actual_chunk_opt_mode = H5D_MPIO_LINK_CHUNK;
+        actual_io_mode = H5D_MPIO_CHUNK_COLLECTIVE;
+
+        /* Set the actual chunk opt mode property. */
+        if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME, &actual_chunk_opt_mode) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual chunk opt mode property")
+
         if(H5D_link_chunk_collective_io(io_info, type_info, fm, sum_chunk) < 0)
             HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish linked chunk MPI-IO")
+
+        /* Set the actual io mode property. */
+        if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_IO_MODE_NAME, &actual_io_mode) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual io mode property")
     } /* end if */
     else
     if(io_option == H5D_MULTI_CHUNK_IO) {
+        /* Set the actual chunk opt mode property */
+        actual_chunk_opt_mode = H5D_MPIO_MULTI_CHUNK_NO_OPT;
+        if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME, &actual_chunk_opt_mode) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual chunk opt mode property")
+
         if(H5D_multi_chunk_collective_io_no_opt(io_info, type_info, fm, dx_plist) < 0)
             HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish multiple chunk MPI-IO")
     } /* end if */
     else { /*multiple chunk IOs with opt */
+        actual_chunk_opt_mode = H5D_MPIO_MULTI_CHUNK;
+        if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME, &actual_chunk_opt_mode) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual chunk opt mode property")
+
         if(H5D_multi_chunk_collective_io(io_info, type_info, fm, dx_plist) < 0)
             HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL, "couldn't finish optimized multiple chunk MPI-IO")
     } /* end else */
@@ -1036,6 +1085,7 @@ H5D_multi_chunk_collective_io(H5D_io_info_t *io_info, const H5D_type_info_t *typ
     int mpi_rank;
 #endif
     size_t              u;                    /* Local index variable */
+    H5D_mpio_actual_io_mode_t actual_io_mode = H5D_MPIO_NO_COLLECTIVE; /* Local variable for tracking the I/O mode used. */
     herr_t              ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_multi_chunk_collective_io)
@@ -1115,6 +1165,15 @@ if(H5DEBUG(D))
             if(chunk_info) {
                 fspace = chunk_info->fspace;
                 mspace = chunk_info->mspace;
+
+                /* Update the local variable tracking the dxpl's actual io mode property.
+                 *
+                 * Note: H5D_MPIO_COLLECTIVE_MULTI | H5D_MPIO_INDEPENDENT = H5D_MPIO_MIXED
+                 *      to ease switching between to mixed I/O without checking the current
+                 *      value of the property. You can see the definition in H5Ppublic.h
+                 */
+                actual_io_mode = actual_io_mode | H5D_MPIO_CHUNK_COLLECTIVE;
+
             } /* end if */
             else {
                 fspace = mspace = NULL;
@@ -1151,6 +1210,9 @@ if(H5DEBUG(D))
             if(chunk_info) {
                 fspace = chunk_info->fspace;
                 mspace = chunk_info->mspace;
+
+                /* Update the local variable tracking the dxpl's actual io mode. */
+                actual_io_mode = actual_io_mode | H5D_MPIO_CHUNK_INDEPENDENT;
             } /* end if */
             else {
                 fspace = mspace = NULL;
@@ -1176,6 +1238,10 @@ if(H5DEBUG(D))
         } /* end else */
     } /* end for */
 
+    /* Write the local value of actual io mode to the DXPL. */
+    if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_IO_MODE_NAME, &actual_io_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual io mode property")
+
 done:
     if(chunk_io_option)
         H5MM_xfree(chunk_io_option);
@@ -1226,6 +1292,7 @@ H5D_multi_chunk_collective_io_no_opt(H5D_io_info_t *io_info,
     int             min_chunk = -1;       /* Minimum # of chunks all processes will operate on */
     int             count_chunk;          /* How many chunks have we operated on? */
     H5D_storage_t   store;                /* union of EFL and chunk pointer in file space */
+    H5D_mpio_actual_io_mode_t actual_io_mode = H5D_MPIO_NO_COLLECTIVE; /*Local variable for tracking the I/O modes used. */
     herr_t          ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI_NOINIT(H5D_multi_chunk_collective_io_no_opt)
@@ -1308,6 +1375,9 @@ if(H5DEBUG(D)) {
             if(H5D_ioinfo_xfer_mode(io_info, dx_plist, H5FD_MPIO_INDEPENDENT) < 0)
                 HGOTO_ERROR(H5E_DATASET, H5E_CANTGET, FAIL, "can't switch to independent I/O")
 
+            /* Update the local variable tracking the dxpl's actual io mode */
+            actual_io_mode = actual_io_mode | H5D_MPIO_CHUNK_INDEPENDENT;
+
             /* Load the chunk into cache and lock it. */
             if((cacheable = H5D_chunk_cacheable(io_info, udata.addr,
                     io_info->op_type == H5D_IO_OP_WRITE)) < 0)
@@ -1364,6 +1434,9 @@ if(H5DEBUG(D)) {
             /* Set up the storage address information for this chunk */
             ctg_store.contig.dset_addr = udata.addr;
 
+            /* Update the local variable tracking the dxpl's actual io Mode. */
+            actual_io_mode = actual_io_mode | H5D_MPIO_CHUNK_COLLECTIVE;
+
             if(H5D_inter_collective_io(&ctg_io_info, type_info, chunk_info->fspace, chunk_info->mspace) < 0)
                 HGOTO_ERROR(H5E_IO, H5E_CANTGET, FAIL,"couldn't finish shared collective MPI-IO")
         } /* end else */
@@ -1376,6 +1449,10 @@ if(H5DEBUG(D)) {
         chunk_node = H5SL_next(chunk_node);
     } /* end while */
 
+    /* Write the local value of actual io mode to the DXPL. */
+    if(H5P_set(dx_plist, H5D_MPIO_ACTUAL_IO_MODE_NAME, &actual_io_mode) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTSET, FAIL, "couldn't set actual io mode property")
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_multi_chunk_collective_io_no_opt */
diff --git a/src/H5Dprivate.h b/src/H5Dprivate.h
index cc770df..a4dddf5 100644
--- a/src/H5Dprivate.h
+++ b/src/H5Dprivate.h
@@ -72,6 +72,8 @@
 #define H5D_XFER_MPIO_CHUNK_OPT_HARD_NAME "mpio_chunk_opt_hard"
 #define H5D_XFER_MPIO_CHUNK_OPT_NUM_NAME "mpio_chunk_opt_num"
 #define H5D_XFER_MPIO_CHUNK_OPT_RATIO_NAME "mpio_chunk_opt_ratio"
+#define H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME "actual_chunk_opt_mode"
+#define H5D_MPIO_ACTUAL_IO_MODE_NAME    "actual_io_mode"
 #endif /* H5_HAVE_PARALLEL */
 #define H5D_XFER_EDC_NAME               "err_detect"    /* EDC */
 #define H5D_XFER_FILTER_CB_NAME         "filter_cb"     /* Filter callback function */
diff --git a/src/H5Fsuper_cache.c b/src/H5Fsuper_cache.c
index 56f9219..cb4ee0e 100644
--- a/src/H5Fsuper_cache.c
+++ b/src/H5Fsuper_cache.c
@@ -469,7 +469,7 @@ H5F_sblock_load(H5F_t *f, hid_t dxpl_id, haddr_t UNUSED addr, void *_udata)
 
     /* (Account for the stored EOA being absolute offset -QAK) */
     if((eof + sblock->base_addr) < stored_eoa)
-        HGOTO_ERROR(H5E_FILE, H5E_TRUNCATED, NULL, "truncated file")
+        HGOTO_ERROR(H5E_FILE, H5E_TRUNCATED, NULL, "truncated file: eof = %llu, sblock->base_addr = %llu, stored_eoa = %llu", (unsigned long long)eof, (unsigned long long)sblock->base_addr, (unsigned long long)stored_eoa)
 
     /*
      * Tell the file driver how much address space has already been
diff --git a/src/H5Pdxpl.c b/src/H5Pdxpl.c
index 8530b8b..3408ced 100644
--- a/src/H5Pdxpl.c
+++ b/src/H5Pdxpl.c
@@ -98,14 +98,20 @@
 #define H5D_XFER_MPIO_CHUNK_OPT_HARD_DEF        H5FD_MPIO_CHUNK_DEFAULT
 #define H5D_XFER_MPIO_CHUNK_OPT_NUM_SIZE        sizeof(unsigned)
 #define H5D_XFER_MPIO_CHUNK_OPT_NUM_DEF         H5D_ONE_LINK_CHUNK_IO_THRESHOLD
-#define H5D_XFER_MPIO_CHUNK_OPT_RATIO_SIZE       sizeof(unsigned)
+#define H5D_XFER_MPIO_CHUNK_OPT_RATIO_SIZE      sizeof(unsigned)
 #define H5D_XFER_MPIO_CHUNK_OPT_RATIO_DEF       H5D_MULTI_CHUNK_IO_COL_THRESHOLD
+/* Definitions for chunk opt mode property. */
+#define H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_SIZE     sizeof(H5D_mpio_actual_chunk_opt_mode_t)
+#define H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_DEF      H5D_MPIO_NO_CHUNK_OPTIMIZATION
+/* Definitions for chunk io mode property. */
+#define H5D_MPIO_ACTUAL_IO_MODE_SIZE    sizeof(H5D_mpio_actual_io_mode_t)
+#define H5D_MPIO_ACTUAL_IO_MODE_DEF     H5D_MPIO_NO_COLLECTIVE
 /* Definitions for EDC property */
-#define H5D_XFER_EDC_SIZE       sizeof(H5Z_EDC_t)
-#define H5D_XFER_EDC_DEF        H5Z_ENABLE_EDC
+#define H5D_XFER_EDC_SIZE           sizeof(H5Z_EDC_t)
+#define H5D_XFER_EDC_DEF            H5Z_ENABLE_EDC
 /* Definitions for filter callback function property */
-#define H5D_XFER_FILTER_CB_SIZE       sizeof(H5Z_cb_t)
-#define H5D_XFER_FILTER_CB_DEF        {NULL,NULL}
+#define H5D_XFER_FILTER_CB_SIZE     sizeof(H5Z_cb_t)
+#define H5D_XFER_FILTER_CB_DEF      {NULL,NULL}
 /* Definitions for type conversion callback function property */
 #define H5D_XFER_CONV_CB_SIZE       sizeof(H5T_conv_cb_t)
 #define H5D_XFER_CONV_CB_DEF        {NULL,NULL}
@@ -205,6 +211,8 @@ H5P_dxfr_reg_prop(H5P_genclass_t *pclass)
     H5FD_mpio_collective_opt_t def_mpio_collective_opt_mode = H5D_XFER_MPIO_COLLECTIVE_OPT_DEF;
     unsigned def_mpio_chunk_opt_num = H5D_XFER_MPIO_CHUNK_OPT_NUM_DEF;
     unsigned def_mpio_chunk_opt_ratio = H5D_XFER_MPIO_CHUNK_OPT_RATIO_DEF;
+    H5D_mpio_actual_chunk_opt_mode_t def_mpio_actual_chunk_opt_mode = H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_DEF;
+    H5D_mpio_actual_io_mode_t def_mpio_actual_io_mode = H5D_MPIO_ACTUAL_IO_MODE_DEF;
 #endif /* H5_HAVE_PARALLEL */
     H5Z_EDC_t enable_edc = H5D_XFER_EDC_DEF;            /* Default value for EDC property */
     H5Z_cb_t filter_cb = H5D_XFER_FILTER_CB_DEF;        /* Default value for filter callback */
@@ -268,7 +276,7 @@ H5P_dxfr_reg_prop(H5P_genclass_t *pclass)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 
 #ifdef H5_HAVE_PARALLEL
-    /* Register the I/O transfer mode property */
+    /* Register the I/O transfer mode properties */
     if(H5P_register_real(pclass, H5D_XFER_IO_XFER_MODE_NAME, H5D_XFER_IO_XFER_MODE_SIZE, &def_io_xfer_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
     if(H5P_register_real(pclass, H5D_XFER_MPIO_COLLECTIVE_OPT_NAME, H5D_XFER_MPIO_COLLECTIVE_OPT_SIZE, &def_mpio_collective_opt_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
@@ -279,6 +287,14 @@ H5P_dxfr_reg_prop(H5P_genclass_t *pclass)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
     if(H5P_register_real(pclass, H5D_XFER_MPIO_CHUNK_OPT_RATIO_NAME, H5D_XFER_MPIO_CHUNK_OPT_RATIO_SIZE, &def_mpio_chunk_opt_ratio, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
         HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
+    /* Register the chunk optimization mode property. */
+    if(H5P_register_real(pclass, H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME, H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_SIZE, &def_mpio_actual_chunk_opt_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
+
+    /* Register the actual io mode property. */
+    if(H5P_register_real(pclass, H5D_MPIO_ACTUAL_IO_MODE_NAME, H5D_MPIO_ACTUAL_IO_MODE_SIZE, &def_mpio_actual_io_mode, NULL, NULL, NULL, NULL, NULL, NULL, NULL) < 0)
+        HGOTO_ERROR(H5E_PLIST, H5E_CANTINSERT, FAIL, "can't insert property into class")
 #endif /* H5_HAVE_PARALLEL */
 
     /* Register the EDC property */
@@ -1483,3 +1499,74 @@ done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Pget_hyper_vector_size() */
 
+
+#ifdef H5_HAVE_PARALLEL
+/*-------------------------------------------------------------------------
+ * Function:	H5Pget_mpio_actual_chunk_opt_mode
+ *
+ * Purpose:	Retrieves the chunked io optimization scheme that library chose
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Jacob Gruber
+ *              Wednesday, May 4, 2011
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_mpio_actual_chunk_opt_mode(hid_t plist_id, H5D_mpio_actual_chunk_opt_mode_t *actual_chunk_opt_mode)
+{
+    H5P_genplist_t     *plist;
+    herr_t ret_value = SUCCEED;   /* return value */
+    
+    FUNC_ENTER_API(H5Pget_mpio_actual_chunk_opt_mode, FAIL)
+    H5TRACE2("e","ix", plist_id, actual_chunk_opt_mode);
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(plist_id, H5P_DATASET_XFER)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Return values */
+    if(actual_chunk_opt_mode)
+        if(H5P_get(plist, H5D_MPIO_ACTUAL_CHUNK_OPT_MODE_NAME, actual_chunk_opt_mode) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get value")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_mpio_actual_chunk_opt_mode() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5Pget_mpio_actual_io_mode
+ *
+ * Purpose:	Retrieves the type of I/O actually preformed when collective I/O
+ *		is requested.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Jacob Gruber
+ *              Wednesday, May 4, 2011
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Pget_mpio_actual_io_mode(hid_t plist_id, H5D_mpio_actual_io_mode_t * actual_io_mode)
+{
+    H5P_genplist_t     *plist;
+    herr_t ret_value = SUCCEED;   /* return value */
+    
+    FUNC_ENTER_API(H5Pget_mpio_actual_io_mode, FAIL)
+    H5TRACE2("e","ix", plist_id, actual_io_mode);
+
+    /* Get the plist structure */
+    if(NULL == (plist = H5P_object_verify(plist_id, H5P_DATASET_XFER)))
+        HGOTO_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "can't find object for ID")
+
+    /* Return values */
+    if(actual_io_mode)
+        if(H5P_get(plist, H5D_MPIO_ACTUAL_IO_MODE_NAME, actual_io_mode) < 0)
+            HGOTO_ERROR(H5E_PLIST, H5E_CANTGET, FAIL, "unable to get value")
+
+done:
+    FUNC_LEAVE_API(ret_value)
+} /* end H5Pget_mpio_actual_io_mode() */
+#endif /* H5_HAVE_PARALLEL */
+
diff --git a/src/H5Ppublic.h b/src/H5Ppublic.h
index 80c028a..492a468 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -120,6 +120,38 @@ typedef H5P_prp_cb1_t H5P_prp_close_func_t;
 /* Define property list iteration function type */
 typedef herr_t (*H5P_iterate_t)(hid_t id, const char *name, void *iter_data);
 
+/* Actual IO mode property */
+typedef enum H5D_mpio_actual_chunk_opt_mode_t {
+    /* The default value, H5D_MPIO_NO_CHUNK_OPTIMIZATION, is used for all I/O
+     * operations that do not use chunk optimizations, including non-collective
+     * I/O and contiguous collective I/O.
+     */
+    H5D_MPIO_NO_CHUNK_OPTIMIZATION = 0,
+    H5D_MPIO_LINK_CHUNK,
+    H5D_MPIO_MULTI_CHUNK,
+    H5D_MPIO_MULTI_CHUNK_NO_OPT
+}  H5D_mpio_actual_chunk_opt_mode_t;
+
+typedef enum H5D_mpio_actual_io_mode_t {
+    /* The following four values are conveniently defined as a bit field so that
+     * we can switch from the default to indpendent or collective and then to
+     * mixed without having to check the original value. 
+     * 
+     * NO_COLLECTIVE means that either collective I/O wasn't requested or that 
+     * no I/O took place.
+     *
+     * CHUNK_INDEPENDENT means that collective I/O was requested, but the
+     * chunk optimization scheme chose independent I/O for each chunk.
+     */
+    H5D_MPIO_NO_COLLECTIVE = 0x0,
+    H5D_MPIO_CHUNK_INDEPENDENT = 0x1,
+    H5D_MPIO_CHUNK_COLLECTIVE = 0x2,
+    H5D_MPIO_CHUNK_MIXED = 0x1 | 0x2,
+
+    /* The contiguous case is separate from the bit field. */
+    H5D_MPIO_CONTIGUOUS_COLLECTIVE = 0x4
+} H5D_mpio_actual_io_mode_t; 
+
 /********************/
 /* Public Variables */
 /********************/
@@ -359,6 +391,10 @@ H5_DLL herr_t H5Pset_type_conv_cb(hid_t dxpl_id, H5T_conv_except_func_t op, void
 H5_DLL herr_t H5Pget_type_conv_cb(hid_t dxpl_id, H5T_conv_except_func_t *op, void** operate_data);
 H5_DLL herr_t H5Pset_enum_conv_overflow(hid_t plist_id, hbool_t conv_overflow);
 H5_DLL herr_t H5Pget_enum_conv_overflow(hid_t plist_id, hbool_t *conv_overflow/*out*/);
+#ifdef H5_HAVE_PARALLEL
+H5_DLL herr_t H5Pget_mpio_actual_chunk_opt_mode(hid_t plist_id, H5D_mpio_actual_chunk_opt_mode_t *actual_chunk_opt_mode);
+H5_DLL herr_t H5Pget_mpio_actual_io_mode(hid_t plist_id, H5D_mpio_actual_io_mode_t *actual_io_mode);
+#endif /* H5_HAVE_PARALLEL */
 
 /* Link creation property list (LCPL) routines */
 H5_DLL herr_t H5Pset_create_intermediate_group(hid_t plist_id, unsigned crt_intmd);
diff --git a/testpar/t_dset.c b/testpar/t_dset.c
index 21e25b6..d2f061d 100644
--- a/testpar/t_dset.c
+++ b/testpar/t_dset.c
@@ -2498,3 +2498,552 @@ none_selection_chunk(void)
     if(data_origin) free(data_origin);
     if(data_array) free(data_array);
 }
+
+
+/* Function: test_actual_io_mode
+ *
+ * Purpose: tests one specific case of collective I/O and checks that the 
+ *          actual_chunk_opt_mode property and the actual_io_mode
+ *          properties in the DXPL have the correct values.
+ *
+ * Input:   selection_mode: changes the way processes select data from the space, as well
+ *          as some dxpl flags to get collective I/O to break in different ways.
+ *          
+ *          The relevant I/O function and expected response for each mode:
+ *              TEST_ACTUAL_IO_MULTI_CHUNK_IND:
+ *                  H5D_mpi_chunk_collective_io, each process reports independent I/O
+ *              
+ *              TEST_ACTUAL_IO_MULTI_CHUNK_COL:
+ *                  H5D_mpi_chunk_collective_io, each process reports collective I/O
+ *
+ *              TEST_ACTUAL_IO_MULTI_CHUNK_MIX:
+ *                  H5D_mpi_chunk_collective_io, each process reports mixed I/O
+ *
+ *              TEST_ACTUAL_IO_MULTI_CHUNK_MIX_DISAGREE:
+ *                  H5D_mpi_chunk_collective_io, processes disagree. The root reports
+ *                  collective, the rest report independent I/O
+ *
+ *              TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_COL:
+ *                  H5D_mpi_chunk_collective_io_no_opt, each process reports collective I/O
+ *
+ *              TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_MIX_DISAGREE:
+ *                  H5D_mpi_chunk_collective_io_no_opt, processes disagree
+ *                  (collective and mixed I/O)
+ *
+ *              TEST_ACTUAL_IO_LINK_CHUNK:
+ *                  H5D_link_chunk_collective_io, processes report linked chunk I/O
+ *
+ *              TEST_ACTUAL_IO_CONTIGUOUS:
+ *                  H5D_contig_collective_write or H5D_contig_collective_read
+ *                  each process reports contiguous collective I/O
+ *
+ *              TEST_ACTUAL_IO_NO_COLLECTIVE:
+ *                  Simple independent I/O. This tests that the defaults are properly set.
+ *
+ *              TEST_ACTUAL_IO_RESET:
+ *                  Perfroms collective and then independent I/O wit hthe same dxpl to
+ *                  make sure the peroperty is correctly reset to the default on each use.
+ *                  Specifically, this test runs TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_MIX_DISAGREE
+ *                  (The most complex case that works on all builds) and then performs
+ *                  an independent read and write with the same dxpls.
+ *
+ *          It may seem like TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_IND and 
+ *          TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_MIX have been accidentally
+ *          left out. This is intentional; the other test cases sufficiently
+ *          cover all cases for Multi Chunk No Opt I/O.
+ * 
+ * Programmer: Jacob Gruber
+ * Date: 2011-04-06
+ */
+static void 
+test_actual_io_mode(int selection_mode) {
+    H5D_mpio_actual_chunk_opt_mode_t   actual_chunk_opt_mode_write = -1;
+    H5D_mpio_actual_chunk_opt_mode_t   actual_chunk_opt_mode_read = -1;
+    H5D_mpio_actual_chunk_opt_mode_t   actual_chunk_opt_mode_expected = -1;
+    H5D_mpio_actual_io_mode_t   actual_io_mode_write = -1;
+    H5D_mpio_actual_io_mode_t   actual_io_mode_read = -1;
+    H5D_mpio_actual_io_mode_t   actual_io_mode_expected = -1;
+    const char  * filename;
+    const char  * test_name;
+    hbool_t     multi_chunk_no_opt;
+    hbool_t     multi_chunk_with_opt;
+    hbool_t     is_chunked;
+    hbool_t     is_collective;
+    int         mpi_size = -1; 
+    int         mpi_rank = -1;
+    int         length;
+    int         * buffer;
+    int         i;
+    MPI_Comm    mpi_comm = MPI_COMM_NULL;
+    MPI_Info    mpi_info = MPI_INFO_NULL;
+    hid_t       fid = -1;
+    hid_t       sid = -1;
+    hid_t       dataset = -1;
+    hid_t       data_type = H5T_NATIVE_INT;
+    hid_t       fapl = -1;
+    hid_t       mem_space = -1;
+    hid_t       file_space = -1;
+    hid_t       dcpl = -1;
+    hid_t       dxpl_write = -1;
+    hid_t       dxpl_read = -1;
+    hsize_t     dims[RANK];
+    hsize_t     chunk_dims[RANK];
+    hsize_t     start[RANK];
+    hsize_t     stride[RANK];
+    hsize_t     count[RANK];
+    hsize_t     block[RANK];
+    hbool_t     use_gpfs = FALSE;
+    herr_t      ret;
+   
+    /* Set up some flags to make some future if statements slightly more readable */
+    multi_chunk_no_opt = (
+        selection_mode == TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_IND ||
+        selection_mode == TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_COL ||
+        selection_mode == TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_MIX_DISAGREE );
+    
+    /* Note: RESET performs the same tests as MULTI_CHUNK_MIX_DISAGREE and then
+     * tests independent I/O
+     */
+    multi_chunk_with_opt = (
+        selection_mode == TEST_ACTUAL_IO_MULTI_CHUNK_IND ||
+        selection_mode == TEST_ACTUAL_IO_MULTI_CHUNK_COL ||
+        selection_mode == TEST_ACTUAL_IO_MULTI_CHUNK_MIX ||
+        selection_mode == TEST_ACTUAL_IO_MULTI_CHUNK_MIX_DISAGREE ||
+        selection_mode == TEST_ACTUAL_IO_RESET );
+ 
+    is_chunked = (
+        selection_mode != TEST_ACTUAL_IO_CONTIGUOUS &&
+        selection_mode != TEST_ACTUAL_IO_NO_COLLECTIVE);
+    
+    is_collective = selection_mode != TEST_ACTUAL_IO_NO_COLLECTIVE;
+
+    /* Set up MPI parameters */
+    MPI_Comm_size(MPI_COMM_WORLD, &mpi_size);
+    MPI_Comm_rank(MPI_COMM_WORLD, &mpi_rank);
+
+    MPI_Barrier(MPI_COMM_WORLD);
+    
+    HDassert(mpi_size >= 1);
+
+    mpi_comm = MPI_COMM_WORLD;
+    mpi_info = MPI_INFO_NULL;
+
+    filename = (const char *)GetTestParameters();
+    HDassert(filename != NULL);
+
+    /* Setup the file access template */
+    fapl = create_faccess_plist(mpi_comm, mpi_info, facc_type, use_gpfs);
+    VRFY((fapl >= 0), "create_faccess_plist() succeeded");
+
+    /* Create the file */
+    fid = H5Fcreate(filename, H5F_ACC_TRUNC, H5P_DEFAULT, fapl);
+    VRFY((fid >= 0), "H5Fcreate succeeded");
+
+    /* Create the basic Space */    
+    dims[0] = dim0;
+    dims[1] = dim1;
+    sid = H5Screate_simple (RANK, dims, NULL);
+    VRFY((sid >= 0), "H5Screate_simple succeeded");
+
+    /* Create the dataset creation plist */
+    dcpl = H5Pcreate(H5P_DATASET_CREATE);
+    VRFY((dcpl >= 0), "dataset creation plist created successfully");
+
+    /* If we are not testing contiguous datasets */
+    if(is_chunked) {
+        /* Set up chunk information.  */
+        chunk_dims[0] = dims[0]/mpi_size;
+        chunk_dims[1] = dims[1];
+        ret = H5Pset_chunk(dcpl, 2, chunk_dims);
+        VRFY((ret >= 0),"chunk creation property list succeeded");
+    }
+
+    /* Create the dataset */
+    dataset = H5Dcreate2(fid, "actual_io", data_type, sid, H5P_DEFAULT,
+            dcpl, H5P_DEFAULT);
+    VRFY((dataset >= 0), "H5Dcreate2() dataset succeeded");
+
+    /* Create the file dataspace */
+    file_space = H5Dget_space(dataset);
+    VRFY((file_space >= 0), "H5Dget_space succeeded");
+
+    /* Choose a selection method based on the type of I/O we want to occur, 
+     * and also set up some selection-dependeent test info. */
+    switch(selection_mode) {
+        
+        /* Independent I/O with optimization */
+        case TEST_ACTUAL_IO_MULTI_CHUNK_IND:
+            /* Since the dataset is chunked by row and each process selects a row,
+             * each process  writes to a different chunk. This forces all I/O to be
+             * independent.
+             */
+            slab_set(mpi_rank, mpi_size, start, count, stride, block, BYROW);
+            
+            test_name = "Multi Chunk - Independent";
+            actual_chunk_opt_mode_expected = H5D_MPIO_MULTI_CHUNK;
+            actual_io_mode_expected = H5D_MPIO_CHUNK_INDEPENDENT;
+            break;
+
+        /* Collective I/O with optimization */
+        case TEST_ACTUAL_IO_MULTI_CHUNK_COL:
+            /* The dataset is chunked by rows, so each process takes a column which
+             * spans all chunks. Since the processes write non-overlapping regular
+             * selections to each chunk, the operation is purely collective.
+             */
+            slab_set(mpi_rank, mpi_size, start, count, stride, block, BYCOL);
+            
+            test_name = "Multi Chunk - Collective";
+            actual_chunk_opt_mode_expected = H5D_MPIO_MULTI_CHUNK;
+            actual_io_mode_expected = H5D_MPIO_CHUNK_COLLECTIVE;
+            break;
+        
+        /* Mixed I/O with optimization */
+        case TEST_ACTUAL_IO_MULTI_CHUNK_MIX:
+            /* A chunk will be assigned collective I/O only if it is selected by each
+             * process. To get mixed I/O, have the root select all chunks and each
+             * subsequent process select the first and nth chunk. The first chunk,
+             * accessed by all, will be assigned collective I/O while each other chunk
+             * will be accessed only by the root and the nth procecess and will be
+             * assigned independent I/O. Each process will access one chunk collectively
+             * and at least one chunk independently, reporting mixed I/O.
+             */
+           
+            if(mpi_rank == 0) {
+                 /* Select the first column */
+                 slab_set(mpi_rank, mpi_size, start, count, stride, block, BYCOL);
+            } else {
+                /* Select the first and the nth chunk in the nth column */
+                block[0] = dim0 / mpi_size;
+                block[1] = dim1 / mpi_size;
+                count[0] = 2;
+                count[1] = 1;
+                stride[0] = mpi_rank * block[0];
+                stride[1] = 1;
+                start[0] = 0;
+                start[1] = mpi_rank*block[1];
+            }
+                
+            test_name = "Multi Chunk - Mixed";
+            actual_chunk_opt_mode_expected = H5D_MPIO_MULTI_CHUNK;
+            actual_io_mode_expected = H5D_MPIO_CHUNK_MIXED;
+            break;
+
+        /* RESET tests that the properties are properly reset to defaults each time I/O is
+         * performed. To acheive this, we have RESET perform collective I/O (which would change
+         * the values from the defaults) followed by independent I/O (which should report the
+         * default values). RESET doesn't need to have a unique selection, so we reuse
+         * MULTI_CHUMK_MIX_DISAGREE, which was chosen because it is a complex case that works 
+         * on all builds. The independent section of RESET can be found at the end of this function.
+         */
+        case TEST_ACTUAL_IO_RESET:
+
+        /* Mixed I/O with optimization and internal disagreement */
+        case TEST_ACTUAL_IO_MULTI_CHUNK_MIX_DISAGREE:
+            /* A chunk will be assigned collective I/O only if it is selected by each
+             * process. To get mixed I/O with disagreement, assign process n to the
+             * first chunk and the nth chunk. The first chunk, selected by all, is 
+             * assgigned collective I/O, while each other process gets independent I/O.
+             * Since the root process with only access the first chunk, it will report
+             * collective I/O. The subsequent processes will access the first chunk
+             * collectively, and their other chunk indpendently, reporting mixed I/O.
+             */
+
+            if(mpi_rank == 0) {
+                 /* Select the first chunk in the first column */
+                 slab_set(mpi_rank, mpi_size, start, count, stride, block, BYCOL);
+                 block[0] = block[0] / mpi_size;
+            } else {
+                /* Select the first and the nth chunk in the nth column */
+                block[0] = dim0 / mpi_size;
+                block[1] = dim1 / mpi_size;
+                count[0] = 2;
+                count[1] = 1;
+                stride[0] = mpi_rank * block[0];
+                stride[1] = 1;
+                start[0] = 0;
+                start[1] = mpi_rank*block[1];
+            }
+            
+            /* If the testname was not already set by the RESET case */
+            if (selection_mode == TEST_ACTUAL_IO_RESET)
+                test_name = "RESET";
+            else
+                test_name = "Multi Chunk - Mixed (Disagreement)";
+            
+            actual_chunk_opt_mode_expected = H5D_MPIO_MULTI_CHUNK;
+               
+            if(mpi_rank == 0)
+                actual_io_mode_expected = H5D_MPIO_CHUNK_COLLECTIVE;
+            else
+                actual_io_mode_expected = H5D_MPIO_CHUNK_MIXED;
+            
+            break; 
+
+        /* Collective I/O without optimization */
+        case TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_COL:
+            /* The dataset is chunked by rows, so when each process takes a column, its
+             * selection spans all chunks. Since no process writes more chunks than any
+             * other, colective I/O is never broken. */ 
+            slab_set(mpi_rank, mpi_size, start, count, stride, block, BYCOL);
+                
+            test_name = "Multi Chunk No Opt - Collective";
+            actual_chunk_opt_mode_expected = H5D_MPIO_MULTI_CHUNK_NO_OPT;
+            actual_io_mode_expected = H5D_MPIO_CHUNK_COLLECTIVE;
+            break;
+       
+
+        /* Mixed I/O without optimization with disagreement */
+        case TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_MIX_DISAGREE:
+            /* Each process takes a column, but the root's column is shortened so that
+             * it only reads the first chunk. Since all the other processes are writing
+             * to more chunks, they will break collective after the first chunk.
+             */
+            slab_set(mpi_rank, mpi_size, start, count, stride, block, BYCOL);
+            if(mpi_rank == 0) 
+                  block[0] = block[0] / mpi_size;
+                
+            test_name = "Multi Chunk No Opt - Mixed (Disagreement)";
+            actual_chunk_opt_mode_expected = H5D_MPIO_MULTI_CHUNK_NO_OPT;
+
+            if(mpi_rank == 0)
+                actual_io_mode_expected = H5D_MPIO_CHUNK_COLLECTIVE;
+            else
+                actual_io_mode_expected = H5D_MPIO_CHUNK_MIXED;
+
+            break;
+        
+        /* Linked Chunk I/O */
+        case TEST_ACTUAL_IO_LINK_CHUNK:        
+            /* Nothing special; link chunk I/O is forced in the dxpl settings. */
+            slab_set(mpi_rank, mpi_size, start, count, stride, block, BYROW);
+              
+            test_name = "Link Chunk";
+            actual_chunk_opt_mode_expected = H5D_MPIO_LINK_CHUNK;
+            actual_io_mode_expected = H5D_MPIO_CHUNK_COLLECTIVE;
+            break;
+
+        /* Contiguous Dataset */
+        case TEST_ACTUAL_IO_CONTIGUOUS:
+            /* A non overlapping, regular selection in a contiguous dataset leads to
+             * collective I/O */
+            slab_set(mpi_rank, mpi_size, start, count, stride, block, BYROW);
+                
+            test_name = "Contiguous";
+            actual_chunk_opt_mode_expected = H5D_MPIO_NO_CHUNK_OPTIMIZATION;
+            actual_io_mode_expected = H5D_MPIO_CONTIGUOUS_COLLECTIVE;
+            break;
+
+        case TEST_ACTUAL_IO_NO_COLLECTIVE:
+            slab_set(mpi_rank, mpi_size, start, count, stride, block, BYROW);
+                
+            test_name = "Independent";
+            actual_chunk_opt_mode_expected = H5D_MPIO_NO_CHUNK_OPTIMIZATION;
+            actual_io_mode_expected = H5D_MPIO_NO_COLLECTIVE;
+            break;
+
+        default:
+            test_name = "Undefined Selection Mode";
+            actual_chunk_opt_mode_expected = -1;
+            actual_io_mode_expected = -1;
+            break;
+    }
+
+    /* Reset the expected values to defulats if the MPI_POSIX driver is in use. 
+     * This property is defined only for mpio, not MPI POSIX. */
+    if (facc_type == FACC_MPIPOSIX) {
+        actual_chunk_opt_mode_expected = H5D_MPIO_NO_CHUNK_OPTIMIZATION;
+        actual_io_mode_expected = H5D_MPIO_NO_COLLECTIVE;
+    }
+
+    ret = H5Sselect_hyperslab(file_space, H5S_SELECT_SET, start, stride, count, block);
+    VRFY((ret >= 0), "H5Sset_hyperslab succeeded");
+ 
+    /* Create a memory dataspace mirroring the dataset and select the same hyperslab
+     * as in the file space. 
+     */
+    mem_space = H5Screate_simple (RANK, dims, NULL);
+    VRFY((mem_space >= 0), "mem_space created");
+    
+    ret = H5Sselect_hyperslab(mem_space, H5S_SELECT_SET, start, stride, count, block);
+    VRFY((ret >= 0), "H5Sset_hyperslab succeeded");
+
+
+    /* Get the number of elements in the selection */
+    length = dim0 * dim1;
+
+    /* Allocate and initialize the buffer */
+    buffer = (int *)HDmalloc(sizeof(int) * length);
+    VRFY((buffer != NULL), "malloc of buffer succeeded"); 
+    for(i = 0; i < length; i++) 
+        buffer[i] = i;
+
+    /* Set up the dxpl for the write */
+    dxpl_write = H5Pcreate(H5P_DATASET_XFER);
+    VRFY((dxpl_write >= 0), "H5Pcreate(H5P_DATASET_XFER) succeeded");
+    
+    /* Set collective I/O properties in the dxpl. */
+    if(is_collective) {
+        /* Request collective I/O */
+        ret = H5Pset_dxpl_mpio(dxpl_write, H5FD_MPIO_COLLECTIVE);
+        VRFY((ret >= 0), "H5Pset_dxpl_mpio succeeded");
+        
+        /* Set the threshold number of processes per chunk for link chunk I/O
+         * to twice mpi_size. This will prevent the threshold from ever being
+         * met, thus forcing multi chunk io instead of link chunk io.
+         */
+        if(multi_chunk_with_opt) {
+            ret = H5Pset_dxpl_mpio_chunk_opt_num(dxpl_write, (unsigned) mpi_size*2);
+            VRFY((ret >= 0), "H5Pset_dxpl_mpio_chunk_opt_num succeeded");
+
+            ret = H5Pset_dxpl_mpio_chunk_opt_ratio(dxpl_write, (unsigned) 99);
+            VRFY((ret >= 0), "H5Pset_dxpl_mpio_chunk_opt_ratio succeeded");
+        }
+
+        /* Request multi chunk I/O without optimization */
+        if(multi_chunk_no_opt) {
+            ret = H5Pset_dxpl_mpio_chunk_opt(dxpl_write, H5FD_MPIO_CHUNK_MULTI_IO);
+            VRFY((ret >= 0), "H5Pset_dxpl_mpio succeeded");
+        }
+    }
+
+    /* Make a copy of the dxpl to test the read operation */
+    dxpl_read = H5Pcopy(dxpl_write);
+    VRFY((dxpl_read >= 0), "H5Pcopy succeeded");
+
+    /* Write */
+    ret = H5Dwrite(dataset, data_type, mem_space, file_space, dxpl_write, buffer);
+    if(ret < 0) H5Eprint2(H5E_DEFAULT, stdout);
+    VRFY((ret >= 0), "H5Dwrite() dataset multichunk write succeeded");
+
+    /* Retreive Actual io valuess */
+    ret = H5Pget_mpio_actual_io_mode(dxpl_write, &actual_io_mode_write);
+    VRFY((ret >= 0), "retriving actual io mode suceeded" );
+
+    ret = H5Pget_mpio_actual_chunk_opt_mode(dxpl_write, &actual_chunk_opt_mode_write);
+    VRFY((ret >= 0), "retriving actual chunk opt mode succeeded" );
+    
+    /* Read */
+    ret = H5Dread(dataset, data_type, mem_space, file_space, dxpl_read, buffer);
+    if(ret < 0) H5Eprint2(H5E_DEFAULT, stdout);
+    VRFY((ret >= 0), "H5Dread() dataset multichunk read succeeded");
+   
+    /* Retreive Actual io values */
+    ret = H5Pget_mpio_actual_io_mode(dxpl_read, &actual_io_mode_read);
+    VRFY((ret >= 0), "retriving actual io mode succeeded" );
+
+    ret = H5Pget_mpio_actual_chunk_opt_mode(dxpl_read, &actual_chunk_opt_mode_read);
+    VRFY((ret >= 0), "retriving actual chunk opt mode succeeded" );
+
+    /* Check write vs read */
+    VRFY((actual_io_mode_read == actual_io_mode_write),
+        "reading and writing are the same for actual_io_mode");
+    VRFY((actual_chunk_opt_mode_read == actual_chunk_opt_mode_write),
+        "reading and writing are the same for actual_chunk_opt_mode");
+
+    
+    /* Test values */
+    if(actual_chunk_opt_mode_expected != (unsigned) -1 && actual_io_mode_expected != (unsigned) -1) {
+        char message[100];
+        sprintf(message, "Actual Chunk Opt Mode has the correct value for %s.\n",test_name);
+        VRFY((actual_chunk_opt_mode_write == actual_chunk_opt_mode_expected), message);
+        sprintf(message, "Actual IO Mode has the correct value for %s.\n",test_name);
+        VRFY((actual_io_mode_write == actual_io_mode_expected), message);
+    } else {
+        HDfprintf(stderr, "%s %d -> (%d,%d)\n", test_name, mpi_rank,
+            actual_chunk_opt_mode_write, actual_io_mode_write);
+    }
+
+    /* To test that the property is succesfully reset to the default, we perform some
+     * independent I/O after the collective I/O
+     */
+    if (selection_mode == TEST_ACTUAL_IO_RESET) {
+        if (mpi_rank == 0) {
+            /* Switch to independent io */
+            ret = H5Pset_dxpl_mpio(dxpl_write, H5FD_MPIO_INDEPENDENT);
+            VRFY((ret >= 0), "H5Pset_dxpl_mpio succeeded");
+            ret = H5Pset_dxpl_mpio(dxpl_read, H5FD_MPIO_INDEPENDENT);
+            VRFY((ret >= 0), "H5Pset_dxpl_mpio succeeded");
+
+            /* Write */
+            ret = H5Dwrite(dataset, data_type, H5S_ALL, H5S_ALL, dxpl_write, buffer);
+            VRFY((ret >= 0), "H5Dwrite() dataset multichunk write succeeded");
+
+            /* Check Properties */
+            ret = H5Pget_mpio_actual_io_mode(dxpl_write, &actual_io_mode_write);
+            VRFY( (ret >= 0), "retriving actual io mode succeeded" );
+            ret = H5Pget_mpio_actual_chunk_opt_mode(dxpl_write, &actual_chunk_opt_mode_write);
+            VRFY( (ret >= 0), "retriving actual chunk opt mode succeeded" );
+
+            VRFY(actual_chunk_opt_mode_write == H5D_MPIO_NO_CHUNK_OPTIMIZATION,
+             "actual_chunk_opt_mode has correct value for reset write (independent)");
+            VRFY(actual_io_mode_write == H5D_MPIO_NO_COLLECTIVE,
+             "actual_io_mode has correct value for reset write (independent)");
+            
+            /* Read */
+            ret = H5Dread(dataset, data_type, H5S_ALL, H5S_ALL, dxpl_read, buffer);
+            VRFY((ret >= 0), "H5Dwrite() dataset multichunk write succeeded");
+
+            /* Check Properties */
+            ret = H5Pget_mpio_actual_io_mode(dxpl_read, &actual_io_mode_read);
+            VRFY( (ret >= 0), "retriving actual io mode succeeded" );
+            ret = H5Pget_mpio_actual_chunk_opt_mode(dxpl_read, &actual_chunk_opt_mode_read);
+            VRFY( (ret >= 0), "retriving actual chunk opt mode succeeded" );
+            
+            VRFY(actual_chunk_opt_mode_read == H5D_MPIO_NO_CHUNK_OPTIMIZATION,
+             "actual_chunk_opt_mode has correct value for reset read (independent)");
+            VRFY(actual_io_mode_read == H5D_MPIO_NO_COLLECTIVE,
+             "actual_io_mode has correct value for reset read (independent)");
+         }
+    }
+
+    /* Release some resources */
+    ret = H5Sclose(sid);
+    ret = H5Pclose(fapl);
+    ret = H5Pclose(dcpl);
+    ret = H5Pclose(dxpl_write);
+    ret = H5Pclose(dxpl_read);
+    ret = H5Dclose(dataset);
+    ret = H5Sclose(mem_space);
+    ret = H5Sclose(file_space);
+    ret = H5Fclose(fid);
+    HDfree(buffer);
+    return;
+}
+
+
+/* Function: actual_io_mode_tests
+ *
+ * Purpose: Tests all possible cases of the actual_io_mode property. 
+ *
+ * Programmer: Jacob Gruber
+ * Date: 2011-04-06
+ */
+void
+actual_io_mode_tests(void) {
+    int mpi_size = -1;
+    int mpi_rank = -1;
+    MPI_Comm_size(MPI_COMM_WORLD, &mpi_size);
+    MPI_Comm_size(MPI_COMM_WORLD, &mpi_rank);
+    
+    test_actual_io_mode(TEST_ACTUAL_IO_NO_COLLECTIVE);
+    
+    test_actual_io_mode(TEST_ACTUAL_IO_MULTI_CHUNK_IND);
+    test_actual_io_mode(TEST_ACTUAL_IO_MULTI_CHUNK_COL);
+    
+    /* The Multi Chunk Mixed test requires atleast three processes. */
+    if (mpi_size > 2)
+        test_actual_io_mode(TEST_ACTUAL_IO_MULTI_CHUNK_MIX);
+    else
+        HDfprintf(stdout, "Multi Chunk Mixed test requires 3 proceses minimum\n");
+    
+    test_actual_io_mode(TEST_ACTUAL_IO_MULTI_CHUNK_MIX_DISAGREE);
+
+    test_actual_io_mode(TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_COL);
+    test_actual_io_mode(TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_MIX_DISAGREE);
+
+    test_actual_io_mode(TEST_ACTUAL_IO_LINK_CHUNK);
+    test_actual_io_mode(TEST_ACTUAL_IO_CONTIGUOUS);
+ 
+    test_actual_io_mode(TEST_ACTUAL_IO_RESET);
+    return;
+}
diff --git a/testpar/testphdf5.c b/testpar/testphdf5.c
index 07568d4..e3c72ef 100644
--- a/testpar/testphdf5.c
+++ b/testpar/testphdf5.c
@@ -498,6 +498,9 @@ int main(int argc, char **argv)
             "test mpi derived type management", 
             PARATESTFILE);
 
+    AddTest("actualio", actual_io_mode_tests, NULL,
+            "test actual io mode proprerty",
+            PARATESTFILE);
 
     /* Display testing information */
     TestInfo(argv[0]);
diff --git a/testpar/testphdf5.h b/testpar/testphdf5.h
index 2b83047..11656f9 100644
--- a/testpar/testphdf5.h
+++ b/testpar/testphdf5.h
@@ -160,6 +160,19 @@ enum H5TEST_COLL_CHUNK_API {API_NONE=0,API_LINK_HARD,
 #define NPOINTS          4          /* Number of points that will be selected
                                                                 and overwritten */
 
+/* Definitions of the selection mode for the test_actual_io_function. */
+#define TEST_ACTUAL_IO_NO_COLLECTIVE                    0
+#define TEST_ACTUAL_IO_RESET                            1
+#define TEST_ACTUAL_IO_MULTI_CHUNK_IND                  2
+#define TEST_ACTUAL_IO_MULTI_CHUNK_COL                  3
+#define TEST_ACTUAL_IO_MULTI_CHUNK_MIX                  4
+#define TEST_ACTUAL_IO_MULTI_CHUNK_MIX_DISAGREE         5
+#define TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_IND           6
+#define TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_COL           7
+#define TEST_ACTUAL_IO_MULTI_CHUNK_NO_OPT_MIX_DISAGREE  8 
+#define TEST_ACTUAL_IO_LINK_CHUNK                       9
+#define TEST_ACTUAL_IO_CONTIGUOUS                       10
+
 /* Don't erase these lines, they are put here for debugging purposes */
 /*
 #define MSPACE1_RANK     1
@@ -173,9 +186,9 @@ enum H5TEST_COLL_CHUNK_API {API_NONE=0,API_LINK_HARD,
 #define MSPACE_DIM1      8
 #define MSPACE_DIM2      9
 #define NPOINTS          4
+*/ /* end of debugging macro */
 
 
-*/ /* end of debugging macro */
 /* type definitions */
 typedef struct H5Ptest_param_t  /* holds extra test parameters */
 {
@@ -222,6 +235,7 @@ void dataset_readAll(void);
 void extend_readInd(void);
 void extend_readAll(void);
 void none_selection_chunk(void);
+void actual_io_mode_tests(void);
 void test_chunk_alloc(void);
 void test_filter_read(void);
 void compact_dataset(void);