[CentOS] Re: Replacing failed software RAID drive

Tony Mountifield tony at softins.clara.co.uk
Mon Oct 8 13:03:30 UTC 2007

In article <47098D7B.9020104 at gmail.com>,
Les Mikesell <lesmikesell at gmail.com> wrote:
> The only tricky part is what happens to the drive names if you boot with 
> /dev/sda broken (depending on the failure mode) or missing.  If the 
> controller doesn't see it, all of the other drive names will shift up. 
> This normally won't affect md device detection, but you may have a non 
> md device mentioned in /etc/fstab, especially for swap devices.

I normally put swap on a /dev/mdN device too. I have seen different people
say you should and you shouldn't, but my reasoning is this: if I have swap
just on raw partitions, e.g. /dev/sda2 and /dev/sdb2, what happens if a
drive dies while running programs are partly swapped out to the failed
drive? I expect at least that the programs would die, and at worst I might
get a kernel panic.

But if I am swapping to /dev/md2 that contains /dev/sda2 and /dev/sdb2 in
a RAID1 mirror, the swapped-out data is preserved on a drive failure, and
the programs should be able to keep running.

Swapping to /dev/mdN certainly seems to work fine, but I haven't yet had
a drive failure to test!

Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org

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