ZFS scrub 'repaired' pool with no chksum or read errors?

Karl Pielorz kpielorz_lst at tdx.co.uk
Fri Jun 10 12:36:45 UTC 2011

--On 10 June 2011 02:33 -0700 Jeremy Chadwick <freebsd at jdc.parodius.com> 

> ZFS experts please correct me, but my experience with this has shown me
> that the scrub itself found actual issues while analysing all data on
> the entire pool -- more specifically, I believe READ/WRITE/CKSUM are
> counters used for when errors are encountered during normal (read:
> non-scrub) operations.  It's been a while since I've seen this happen,
> but have seen it on our Solaris 10 machines at my workplace.  I've never
> been sure what it means; possibly signs of "bit rot"?

I'm reasonably sure (and all the documentation I've seen) seems to indicate 
that the checksum/read error columns reflect errors found during either 
normal operations - or scrubs... I've run ZFS on some pretty ropey systems 
during testing, and it certainly seemed to 'tick up' the errors during 

> If you're worried about your disk (ada0), please provide output from
> "smartctl -a /dev/ada0" and I'll be more than happy to review the output
> and provide you with any insights.  I do believe you when you say it
> looks fine, but every model of disk is different in some regard.

I'm not overly worried about the disk or the errors - more curious as to 
why they showed without ticking up anything in the error columns - unless 
it's not meant to.

I can email you the smart output, but there's no pending reallocations, all 
the SMART parameters are well above their thresholds - additionally smartd 
hasn't noticed anything 'changing' on the drive to alert about - the drive 
itself is also reasonably 'new' (and there's no evidence of anything being 
thrown in syslog/dmesg). If I get time later I might offline the drive and 
run a long test on it - if that does anything weird & wonderful, I'll take 
you up on your offer, and email you :-) But like I said, I'm not overly 
concerned, more curious ;)


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