RAID 1 Mismatches
Rick Wagner
rjwgnr27 at verizon.net
Tue Dec 29 03:41:53 UTC 2009
I have three disks in my system, divided into a mix of RAID-1 and RAID-5
partitions. I have /boot as a RAID-1 on MD0 (SDA1, SDB1), / as RAID-1 on MD1
(SDA2, SDB2), and the remainder as RAID-5 with LVM (SDA3, SDB3, SDC3). The
intent is that for boot and root, if SDA fails, I can boot off SDB.
Every week I get an "Anacron job 'cron.weekly'" e-mail telling of: "WARNING:
mismatch_cnt is not 0 on /dev/md1". If I look at
/sys/block/md1/md/mismatch_cnt, I will see a number, usually 128, sometimes
64. If I manually invoke a scan, I will see the same number. Note that
neither MD0 or MD3 report any errors.
If I set SDB1 bad, then remove then re-add it, it will rebuild fine, and a scan
shows no errors. Scanning the messages (current and historical), I see no
reports of medium errors reported for any of SD[ABC].
I have several questions:
1) Where can the errors be coming from? I would understand if a drive were
reporting errors. Could it be during boot, one of the R-1 members is being
written too before MD is started?
2) Sans drive errors messages, how to determine which drive is out of sync. I
have resynced SDA2 to SDB2, but that is basically a coin flip; if SDB2 were
correct, then I may have damaged files on SDA2. How can I determine where the
mismatches occur, and then determine the file(s) potentially affected?
Thanks,
--rick
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