Howdy,
I have at several times had issues with consumer grade PC hardware and ZFS not
getting along. The problem is not the disks but the fact I dont have ECC and
end to end checking on the datapath. What is happening is that random memory
errors and bit flips are written out to disk and when read back again ZFS
reports it as a checksum failure:
pool: myth
state: ONLINE
status: One or more devices has experienced an error resulting in data
corruption. Applications may be affected.
action: Restore the file in question if possible. Otherwise restore the
entire pool from backup.
see: http://www.sun.com/msg/ZFS-8000-8A
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
myth ONLINE 0 0 48
raidz1 ONLINE 0 0 48
c7t1d0 ONLINE 0 0 0
c7t3d0 ONLINE 0 0 0
c6t1d0 ONLINE 0 0 0
c6t2d0 ONLINE 0 0 0
errors: Permanent errors have been detected in the following files:
/myth/tv/1504_20080216203700.mpg
/myth/tv/1509_20080217192700.mpg
Note there are no disk errors, just entire RAID errors. I get the same thing
on a mirror pool where both sides of the mirror have identical errors. All I
can assume is that it was corrupted after the checksum was calculated and
flushed to disk like that. In the past it was a motherboard capacitor that had
popped - but it was enough to generate these errors under load.
At any rate ZFS is doing the right thing by telling me - what I dont like is
that from that point on I cant convince ZFS to ignore it. The data in question
is video files - a bit flip here or there wont matter. But if ZFS reads the
affected block it returns and I/O error and until I restore the file I have no
option but to try and make the application skip over it. If it was UFS for
example I would have never known, but ZFS makes a point of stopping anything
using it - understandably, but annoyingly as well.
What I would like to see is an option to ZFS in the style of the 'onerror' for
UFS i.e the ability to tell ZFS to join fight club - let what doesnt matter
truely slide. For example:
zfs set erroraction=[iofail|log|ignore]
This would default to the current action of "iofail" but in the event you
wanted to try and recover or repair data, you could set log to say generate an
FMA event that there is bad checksums, or ignore, to get on with your day.
As mentioned, I see this as mostly an option to help repair data after the
issue is identified or repaired. Of course its data specific, but if the
application can allow it or handle it, why should ZFS get in the way?
Just a thought.
Cheers,
Adrian
PS: And yes, I am now buying some ECC memory.
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