Apparently spurious ZFS CRC errors (was Re: ZFS data error
without reasons)
Alexander Leidinger
Alexander at Leidinger.net
Wed Mar 25 02:56:30 PDT 2009
Quoting Mark Powell <M.S.Powell at salford.ac.uk> (from Fri, 20 Mar 2009
15:30:11 +0000 (GMT)):
> On Fri, 20 Mar 2009, Mark Powell wrote:
>
>> As this same hardware worked, well with 7 for a long time, and can
>> work perfectly with 8 for several days until the errors strike,
>> this seems like some curious 8 problem?
>
> Hmmm. Perhaps I'm not being fair on 8. Just had a look at my
> loader.conf for 7 and I can see that I used to run with every
> zfs*disable on. I've just rebooted 8 with:
>
> vfs.zfs.cache_flush_disable: 1
> vfs.zfs.mdcomp_disable: 1
> vfs.zfs.prefetch_disable: 1
> vfs.zfs.zil_disable: 1
> hw.ata.wc: 1
>
> The current fs which produced errors on every scrub now reports no errors.
> I now need to find which option fixed it.
> I suspect hw.ata.wc. Is this still a known issue?
I would expect that it is the combination of cache_flush_disable and
zil_disable with the wc enable. If you reenable the zil and the cache
flush, the wc should not cause the problems you see. You may want to
have a look at
http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide
for a more detailed description of what those options are doing (and
why you should not disable those features on normal disks). I also
suggest to not disable the meta-data compression, as it seems it only
affects a small amount of meta-data instead of all meta-data.
If you want to get more out of zfs, maybe vfs.zfs.vdev.max_pending
could help if you are using SATA (as I read the zfs tuning guide, it
makes sense to have a high value when you have command queueing, which
we have with SCSI drives, but not yet with SATA drives and probably
not at all with PATA drives).
Bye,
Alexander.
--
QOTD:
"I am not sure what this is, but an 'F' would only dignify it."
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