Public bug reported:
The NFS Client is ignoring O_SYNC when opening a file.
This bug is causing unstable writes in the application environment even
when the mount option "sync" is set on both sides (NFS client and server).
We have a test case shows that the Ubuntu NFS client does
not submit "nfs_file_sync" write requests when the file open call
includes O_SYNC.
I have strace and tcpdump data showing this issue. The strace shows that
the file is opened with O_SYNC. The tcpdump shows "unstable writes"
which should not occur with either "sync" mount option or with forced
sync by using the open file system call with O_SYNC. Comparing the
tcpdump data between the Ubuntu NFS client a RHEL NFS client shows
that the Ubuntu NFS client does not issue the "nfs_file_sync" write
requests, while the RHEL NFS client does.
This issue does not appear to be tied to a specific model of storage
array or a specific file system. Tests have been performed against an NFS
server having access to a GPFS file system where a SAN attached IBM
DS5300 is the underlying storage array. But the behaviour is exactly
the same when they export a local ext3 file system from the local scsi
disk.
** Affects: nfs-utils (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/709392
Title:
NFS client does not submit "nfs_file_sync" write requests when the
file open call includes O_SYNC.
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