Dennis Clarke wrote:
Another thing to keep an eye out for is disk caching. With ZFS,
whenever the NFS server tells us to make sure something is on disk, we
actually make sure it's on disk by asking the drive to flush dirty data
in its write cache out to the media. Needless to say, this takes a
while.
With UFS, it isn't aware of the extra level of caching, and happily
pretends it's in a world where once the drive ACKs a write, it's on
stable storage.
If you use format(1M) and take a look at whether or not the drive's
write cache is enabled, that should shed some light on this. If it's
on, try turning it off and re-run your NFS tests on ZFS vs. UFS.
Either way, let us know what you find out.
Slightly OT but you just reminded me of why I like disks that have Sun
firmware on them. They never have write cache on. At least I have never
seen it. Read cache yes but write cache never. At least in the Seagates and
Fujitsus Ultra320 SCSI/FCAL disks that have a Sun logo on them.
We turned if off when we could but it was possible to re-enable
it...which I believe ZFS will do.
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