[CentOS] Re: question about software Raid 1

Kanwar Ranbir Sandhu m3freak at thesandhufamily.ca
Wed Oct 1 15:11:20 UTC 2008


On Sun, 2008-09-21 at 21:01 +0200, Kay Diederichs wrote:
> Fact is that with CentOS-5 kernels (but not with CentOS-4, as this 
> functionality became available in kernel 2.6.17) you could (or rather 
> _should_ regularly)
>     echo check > /sys/block/mdX/md/sync_action
> to check agreement between the two (or more) copies. When this finishes, 
> /sys/block/mdX/md/mismatch_cnt shows you the number of mismatches. You 
> can fix these with
>     echo repair > /sys/block/mdX/md/sync_action

Interesting.  I'll give this a go on my own desktop system which is
running RAID 1.

You said above, "When this finishes...", but how do you know the check
is completed?  I saw this in /var/log/messages: 

Oct  1 11:02:47 ranbir kernel: md: data-check of RAID array md0
Oct  1 11:02:47 ranbir kernel: md: minimum _guaranteed_  speed: 1000 KB/sec/disk.
Oct  1 11:02:47 ranbir kernel: md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for data-check.
Oct  1 11:02:47 ranbir kernel: md: using 128k window, over a total of 104320 blocks.
Oct  1 11:02:48 ranbir kernel: md: md0: data-check done.
Oct  1 11:02:48 ranbir kernel: RAID1 conf printout:
Oct  1 11:02:48 ranbir kernel: --- wd:2 rd:2
Oct  1 11:02:48 ranbir kernel: disk 0, wo:0, o:1, dev:sda1
Oct  1 11:02:48 ranbir kernel: disk 1, wo:0, o:1, dev:sdb1

There was nothing else after the last line.  I don't know exactly what
the "disk" lines mean.

Regards,

Ranbir



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