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RE: [Linux-cluster] Software RAID support by GFS



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 redhat com 
> [mailto:linux-cluster-bounces 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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