On Wed, 2006-12-06 at 09:57 -0500, Josef Whiter wrote:
> Hello,
>
> Software RAID has the same limitation as LVM1 as it's not cluster aware. Even
> with LVM2 you have to use CLVM to make sure the appropriate cluster wide locking
> takes place before touching the metadata on the disk. Software RAID has no
> cluster awareness, so you could run into the same problem you would have if you
> mounted an ext3 filesystem RW between two nodes, you would end up with
> corruption. This isn't a limitation with GFS, but more a limitation with md
> RAID, as its not cluster aware. Thank you,
>
I *think* this is because write ordering between parts of a md-raid set
isn't guaranteed... I've actually forgotten how the corruption occurs.
(d'oh!)
e.g. Two guys write to the same md-block at the same time. One writes
in {1 2 3 4 5} order, the other writes in reverse order - the stripe for
that block is now corrupt.
... not to mention cache-coherency problems with md-raid.
-- Lon
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