On Mon, Jul 31, 2006 at 02:17:00PM -0400, Jan Schaumann wrote:
> Is there anybody here who's using ZFS on Apple XRaids and serving them
> via NFS? Does anybody have any other ideas what I could do to solve
> this? (I have, in the mean time, converted the XRaid to plain old UFS,
> and performance is perfectly fine here, but I'd still be interested in
> what exactly is going on.)
One of the main differences in how UFS and ZFS treats a disk is that ZFS
will enable the write cache and send down SYNCHRONIZE_CACHE commands
down to the disk (at appropriate points) to ensure that data hits stable
storage. Also, NFS tends to force this operation quite often. My guess
would be that the Apple XRaid responds "poorly" to these commands,
leading to the clumps of hair that are probably on your floor. :)
To test this theory, run this command on your NFS server (as root):
echo '::spa -v' | mdb -k | \
awk '/dev.dsk/{print $1"::print -a vdev_t vdev_nowritecache"}' | \
mdb -k | awk '{print $1"/W1"}' | mdb -kw
This will turn off write cache flushing on all devices in all pools.
Note that this is a very dangerous state to run in if your disk/RAID
has caching enabled without NVRAM. To put things back to normal, type
the above command, replacing the W1 in the last line with W0.
If this helps, we can start thinking about options for fixing it.
--Bill
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