A performance degradation occurs on a gfs2 filesystem as the load increases on RHEL 6 or RHEL 7

Issue

• A write performance degradation occurs on a gfs2 filesystem as the load increases on RHEL 6 or RHEL 7.
• When running the script called iotest.sh or rhel_iotest.sh (which are provided by SAS as benchmarking tool to test filesystem and storage) the write performance of a gfs2 filesystem decreased as the number of dd processes increased.
• The same problem occurs when doing simultaneous dd commands or large simultaneous data writes using more CPU cores on the same node to the same filesystem.
• This problem has nothing to do with the performance of the storage (though it still needs to be configured properly). It is about the rate a gfs2 filesystem can take write requests and place them into the page cache.
• Performance seems to be capped at around 800-900 MB/sec per gfs2 filesystem.