Sunday, September 6, 2009

Linux software RAID component device mismatches

Somehow my raid array has gotten out of sync, and the monthly check logged this message:

Aug 2 02:42:29 filemaster mdadm[2430]: RebuildFinished event detected on md device /dev/md0, component device mismatches found: 128

I was a bit concerned about this, since this array is a 2-drive mirror, and I don't know how to tell which device is correct. I suppose I'll have to just let the kernel fix the mismatches and hope for the best. Google found some pages that say the way to tell the kernel to rebuild the array is:

echo repair >> /sys/block/md0/md/sync_action

I did that, waited for the rebuild to finish, and then initiated a re-check:

echo check >> /sys/block/md0/md/sync_action

However, once that finished, the same 128 mismatches were still reported.
I think the way to fix it is to make one of the devices as failed, remove it from the array, then re-add it.

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