NFS performance (can't use "async")

[Wipe_Out]

Hi,

Recently I have been testing various options to create a NFS server for
storing virtual machine disk images.. For data integrity sake running as
"async" is not an option and this appears to be the most commonly
recommended "improvement"..

The issue I have is not so much with raw throughput, I have been able to
saturate a 1GbE connections easily.. The issue is more to do with write
operations.. On FreeBSD+ZFS I can get about 800 FSYNCS/s.. On Ubuntu 12.04
(tested with ext3/ext4/XFS/BtrFS) I can only get 15-20.. This is on the
exact same hardware..

I don't think its file system related because of all the file systems ZFS
and BtrFS should have the biggest overhead but switching from ext4 to BtrFS
didn't change the performance results..

I haven't yet tried other distro's to see if the slow NFS is Ubuntu related
but I can't see why is would be..

Does anyone have any ideas why there is such a huge difference between the
performance of the FreeBSD and Ubuntu NFS servers?
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