Uwe Dippel wrote:
Richard Elling wrote:
status: One or more devices has experienced an unrecoverable error. An
attempt was made to correct the error. Applications are unaffected.
NAME STATE READ WRITE CKSUM
rpool ONLINE 0 0 0
c1d0s0 ONLINE 0 0 1
errors: No known data errors
# zpool clear rpool
# zpool status -v
pool: rpool
state: ONLINE
scrub: scrub completed after 0h47m with 0 errors on Tue Apr 14
23:53:48 2009
config:
NAME STATE READ WRITE CKSUM
rpool ONLINE 0 0 0
c1d0s0 ONLINE 0 0 0
errors: No known data errors
Now I wonder where that error came from. It was just a single
checksum error. It couldn't go away with an earlier scrub, and
seemingly left no traces of badness on the drive. Something serious?
At least it looks a tad contradictory: "Applications are
unaffected.", it is unrecoverable, and once cleared, there is no
error left.
Since there are "no known data errors," it was fixed, and the scrub
should succeed without errors. You cannot conclude that the drive
is completely free of faults using scrub, you can only test the areas
of the drive which have active data.
I didn't conclude that.
Could you propose alternate wording?
I conclude, when an 'unrecoverable error' is found, that 'zpool clear'
cannot recover it.
ZFS did recover, which is why it says "no known data errors."
If the data was not recoverable, then it would show you which
file was affected. Perhaps the confusion is the layer which is
reporting the bad data? In the fmdump output, there is a ZFS
checksum mismatch detected. It is unclear why there is a
mismatch because there was not a corresponding error event
logged by the disk driver. What ZFS knows is that the data it
read did not match the data it wrote. So ZFS repaired the data.
Since ZFS is a COW architecture, the repair would involve
writing the corrected data elsewhere.
Still, there was one one CHSUM error before, and it wouldn't go away
before the 'clear'; while after the 'clear' even that one would
disappear.
Clear just resets the counters.
-- richard
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