Re: [Xen-users] XEN and clustering?

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sat, Feb 27, 2010 at 11:07:41AM +0100, Jakov Sosic wrote:
> Hi.
> 
> I'm using Xen on RHEL cluster, and I have strange problems. I gave raw
> volumes from storage to Xen virtual machines. With windows, I have a
> problem that nodes don't see the volume as same one.... for example:
> 
> clusternode1# clusvcadm -d vm:winxp
> clusternode1# dd if=/dev/mapper/winxp of=/node1winxp
> clusternode2# dd if=/dev/mapper/winxp of=/node2winxp
> clusternode3# dd if=/dev/mapper/winxp of=/node3winxp
> 
> When I download these files and diff them, they all three differ.
> 
> Also, sometimes very strange things happen. For example I download some
> file into winxp, shut it down, then start it on another node, and file
> is missing?!?!?!?!
> 
> Should I use maybe CLVM and not raw volumes from storage? Why is this
> happening?
> 

What kind of xen disk backend are you using? phy:? 
What kind of storage are you using? 

When sharing block devices in a cluster across nodes you need
to make absolutely sure there's no caching going on in dom0s,
so that the disk contents are always in-sync.

CLVM only helps with safely managing the LVM metadata, 
not with the actual usage of the volumes.

-- Pasi


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