>>From: Robin Hill
>>Date: 2012-11-26 20:50
>>To: hanguozhong
>>CC: linux-raid
>>Subject: Re: a question about how to repair raid5
>>On Mon Nov 26, 2012 at 08:32:38 +0800, hanguozhong wrote:
> Hi, every one:
> I have a question about how to repair raid5.
> Days ago, I received a email from the monitor of mdadm.
> The email told me that there were lots of mismatch_cnt in the array.
> Then I tried to find the solution of this problem on Google. Most solutions were as the following:
>
> #echo repair /sys/block/md0/md/sync_action
> #echo "check" > /sys/block/md0/md/sync_action
> #cat /sys/block/md0/md/mismatch_cnt
>
> I did repair the array like the above.
> But I found that it took lots of time to "repair" and "check" the array.
> Why there was a "check" after "repair"I did not know. And it spent as much time as "repair".
> Is it redundant? Anyone can help me?
>>That's the correct process, yes. The "check" will verify whether the
>>parity block for each stripe is correct, whereas the "repair" will also
>>rewrite any parity blocks which don't match. You rerun the "check" after
>>the "repair" to ensure that everything has been repaired correctly (if
>>there's still mismatches then it would point towards a problem with your
>>setup somewhere). Both are doing a full read of all disks, so will take
>>about the same time (the number of additional writes that the "repair"
>>needs to do should not impact on the time significantly).
Hmm, I know what you mean. But there is a question I still do not quit understand.
Why "repair" action does not record the blocks that not be repaired, and then
the "check" action will do a full read of all disks again? I do not understand.
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