Merge pull request #596 in HDFFV/hdf5 from GreaterThan-2GB-MPIO to develop

* commit '6a5aa46e936340ed540359290374fa909f9213a6':
  Added a brief outline for Large MPI-IO transfers into RELEASE.txt
  Fix up the ExpressMode check for skipping slow running tests.
  Include code fixes and additional modifications pointed out by code reviewers
  Commited changes to the development branch here to allow a pull request to be published
  Commit changes needed for pull request

1 files changed, 23 insertions, 1 deletions

diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index 20d58b3..4335b37 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -62,7 +62,29 @@ New Features
 
     Parallel Library:
     -----------------
-    -
+    - Large MPI-IO transfers
+
+      Previous releases of PHDF5 would fail when attempting to
+      read or write greater than 2GB of data in a single IO operation.
+      This issue stems principally from an MPI API whose definitions
+      utilize 32 bit integers to describe the number of data elements
+      and datatype that MPI should use to effect a data transfer.
+      Historically, HDF5 has invoked MPI-IO with the number of
+      elements in a contiguous buffer represented as the length
+      of that buffer in bytes.
+
+      Resolving the issue and thus enabling larger MPI-IO transfers
+      is accomplished first, by detecting when a user IO request would
+      exceed the 2GB limit as described above.  Once a transfer request
+      is identified as requiring special handling, PHDF5 now creates a
+      derived datatype consisting of a vector of fixed sized blocks
+      which is in turn wrapped within a single MPI_Type_struct to
+      contain the vector and any remaining data.   The newly created
+      datatype is then used in place of MPI_BYTE and can be used to
+      fulfill the original user request without encountering API
+      errors.
+
+      (RAW – 2017/07/11, HDFFV-8839)
 
     Fortran Library:
     ----------------