On Feb 6, 2007, at 06:55, Robert Milkowski wrote:
Hello zfs-discuss,
It looks like when zfs issues write cache flush commands se3510
actually honors it. I do not have right now spare se3510 to be 100%
sure but comparing nfs/zfs server with se3510 to another nfs/ufs
server with se3510 with "Periodic Cache Flush Time" set to disable
or so longer time I can see that cache utilization on nfs/ufs stays
about 48% while on nfs/zfs it's hardly reaches 20% and every few
seconds goes down to 0 (I guess every txg_time).
nfs/zfs also has worse performance than nfs/ufs.
Does anybody know how to tell se3510 not to honor write cache flush
commands?
I don't think you can .. DKIOCFLUSHWRITECACHE *should* tell the array
to flush the cache. Gauging from the amount of calls that zfs makes to
this vs ufs (fsck, lockfs, mount?) - i think you'll see the
performance diff,
particularly when you hit an NFS COMMIT. (If you don't use vdevs you
may see another difference in zfs as the only place you'll hit is on
the zil)
btw - you may already know, but you'll also fall to write-through on
the cache
if your battery charge drops and we also recommend setting to write-
through
when you only have a single controller since a power event could
result in
data loss. Of course there's a big performance difference between
write-back and write-through cache
---
.je
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