On Jan 27, 2013, at 12:26 PM, Wolfgang Denk [off-list ref] wrote:

I have seen "mismatch_cnt is not 0" warnings in the past, but that has
always been with RAID 1 arrays, and with relatively small numbers on
/sys/block/md*/md/mismatch_cnt; my understanding was that this was not
actually critical.

Well, you have a block on each drive that's supposed to be identical, and if there's a mismatch that means they're not identical and it's ambiguous which one is correct. So if the data on the drives is unimportant to retrieve correctly, then I guess it's not a critical error.

However, after updating to Fedora 18, I get this message from all
updated
systems that have RAID 6 arrays, and with _huge_ numbers of
mismatch_cnt, like that:

fter updating to Fedora 18, I get this message from all updated
systems that have RAID 6 arrays, and with _huge_ numbers of
mismatch_cnt, like that:

Bad paste. No messages provided.

This is with mdadm v3.2.6 (mdadm-3.2.6-7.fc18.x86_64); except for the
huge values of mismatch_cnt, I see no other indications for errors on
the disk drives, RAID arrays or the file systems on top of these.

Is this some known (and hopefully harmless), issue, or must I worry
about our data?

It means there's a mismatch between parity and data. One of them is wrong, maybe both if there are many errors. So yeah I'd say it sounds like a problem.

What's the smartctl -a look like for all drives? I imagine one or more have bad sectors, ECC errors, or UDMA/CRD errors.


Chris Murphy