[OpenIndiana-discuss] ZFS single drive CKSUM errors

[Richard L. Hamilton]

My first guess would be that the errors were in metadata,
which is redundant even with a single disk.  google for

zfs "ditto blocks"

for an explanation.  (if the filesystem has the copies= parameter
set to something higher than the default of 1, data blocks will
also be duplicated on a single disk, with corresponding reduction
in usable space of course)

My second guess would be that some of the errors turned out to
not be real, maybe due to intermittent hardware errors during reads
(which could be anything along the path from disk to RAM, including
either of those).

I'd run a scrub regularly, check /var/adm/messages* for I/O errors,
see if the SMART tools (if they're available or you can compile
them, and they work with the type of disk you have) tell you
anything, and so on.

(My third guess would be that it's a quirk of a bug in the
particular build you're running.  That's usually near the bottom
of my guesses, but there have been some builds of zfs that had some problems, although I don't mean to suggest that your situation
fits any particular bug.)

On Jan 22, 2011, at 5:08 PM, Michelle Knight wrote:

> Hi Folks,
> 
> Something I don't understand.
> 
> A single drive with a ZFS partition on it. No mirror, no raid, no nothing.
> 
> I copied a load of files to it and did a scrub.
> 
> It encountered six checksum errors and was able to recover from them ... 
> without having any mirror or other redundant reference ... it didn't lose a 
> single file.
> 
> Now ... am I mad, or does this mean I've got corruption somewhere, or how did 
> ZFS manage to recover from cksum errors that it detected on a single drive?
> 
> I haven't managed to read anything yet which goes to the depth of explaining 
> this.
> 
> Can someone help me on this please?
> 
> Many thanks,
> 
> Michelle.
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