[Linux-cluster] Software RAID support by GFS
Lin Shen (lshen)
lshen at cisco.com
Wed Dec 6 18:19:35 UTC 2006
One more clarification. As long as I only put partitions from the same
node into a RAID set, the corruption shouldn't happen, right?
lin
> -----Original Message-----
> From: linux-cluster-bounces at redhat.com
> [mailto:linux-cluster-bounces at redhat.com] On Behalf Of Lon Hohberger
> Sent: Wednesday, December 06, 2006 7:45 AM
> To: linux clustering
> Subject: Re: [Linux-cluster] Software RAID support by GFS
>
> 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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