Re: Apparently spurious ZFS CRC errors (was Re: ZFS data error without reasons)

From: Alexander Leidinger <Alexander_at_Leidinger.net>
Date: Wed, 25 Mar 2009 10:56:13 +0100
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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Received on Wed Mar 25 2009 - 08:56:29 UTC

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