On 09/02/09 05:40 AM, Henrik Johansson wrote:
For those of us which have already upgraded and written data to our
raidz pools, are there any risks of inconsistency, wrong checksums in
the pool? Is there a bug id?
This may not be a new problem insofar as it may also affect mirrors.
As part of the ancient "mirrored drives should not have checksum
errors thread", I used Richard Elling's amazing zcksummon script
http://www.richardelling.com/Home/scripts-and-programs-1/zcksummon
to help diagnose this (thanks, Richard, for all your help).
The bottom line is that hardware glitches (as found on cheap PCs
without ECC on buses and memory) can put ZFS into a mode where it
detects bogus checksum errors. If you set copies=2, it seems to
always be able to repair them, but they are never actually repaired.
Every time you scrub, it finds a checksum error on the affected file(s)
and it pretends to repair it (or may fail if you have copies=1 set).
Note: I have not tried this on raidz, only mirrors, where it is
highly reproducible. It would be really interesting to see if
raidz gets results similar to the mirror case when running zcksummon.
Note I have NEVER had this problem on SPARC, only on certain
bargain-basement PCs (used as X-Terminals) which as it turns out
have mobos notorious for not detecting bus parity errors.
If this is the same problem, you can certainly mitigate it by
setting copies=2 and actually copying the files (e.g., by
promoting a snapshot, which I believe will do this - can someone
confirm?). My guess is that snv121 has done something to make
the problem more likely to occur, but the problem itself is
quite old (predates snv100). Could you share with us some details
of your hardware, especially how much memory and if it has ECC
orbus parity?
Cheers -- Frank
On 09/02/09 05:40 AM, Henrik Johansson wrote:
Hi Adam,
On Sep 2, 2009, at 1:54 AM, Adam Leventhal wrote:
Hi James,
After investigating this problem a bit I'd suggest avoiding deploying
RAID-Z
until this issue is resolved. I anticipate having it fixed in build 124.
Regards
Henrik
http://sparcv9.blogspot.com <http://sparcv9.blogspot.com/>
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