High Fragmentation with XFS and NFS Sync

[Stefan Ring]

On Sat, Jul 2, 2016 at 10:52 AM, Nick Fisk <friskyfisk10 at googlemail.com> wrote:
> Hi, hope someone can help me here.
>
> I'm exporting some XFS fs's to ESX via NFS with the sync option enabled. I'm
> seeing really heavy fragmentation when multiple VM's are copied onto the
> share at the same time. I'm also seeing kmem_alloc failures, which is
> probably the biggest problem as this effectively takes everything down.
>

The same thing happens with MySQL's InnoDB files if O_DIRECT is in use.

The kmem_alloc failure taking everything down is most likely a result
of you calling xfs_bmap on these files and does not happen during
normal use. I've had the same experience some time ago.