RE: [Xen-users] Quorum disk problem

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> Hi!
> I have a problem setting up cluster of w2k3 servers. My configurations
> looks like this:
> 
> server1: dom0 (centos5): virtual1 (w2k3)
> server2: dom0 (centos5): virtual2 (w2k3)
> 
> I want to make a cluster with two nodes: virtual1 and virtual2.
> I have a quorum disk set up on SAN, both dom0 configures it via HBA
> (qlogic card with HP driver) as scsi /dev/sdb:
> 
> SAN.quorum -> server1 hba (/dev/sdb) -> virtual1
> SAN.quorum -> server2 hba (/dev/sdb) -> virtual2
> 
> Then it is passed as block device to domU with this xen config:
> 
> disk = [ ..<other disks>..., 'phy:/dev/sdb:sdb:w' ]
> 
> Everything would be fine except that changes made to quorum disk
> on active node are not seen after changing active node to the other
> one. It looks like all changes are cached somewhere and active node
> writes to this same disk as it would be two different disks. After
> rebooting both nodes only changes from first active node are written to
> disk.
> 
> Could you please help me in setting up the quorum disk ?

I have suggested on this list previously that I think the qemu code makes use 
of Dom0's buffer cache. This makes the performance look artificially better, 
and has the drawback that data isn't actually written to disk immediately, 
which would give you the symptoms you are seeing.

I haven't had any confirmation of this suggestion from anyone who would know 
for sure though.

You could try using the GPL PV drivers I wrote. If you are using SMP then you'd 
better try the latest pre-release which I can't break easily under SMP (the 
previous version would break and damage your filesystem under SMP :)

http://www.meadowcourt.org/WindowsXenPV-0.7.0-pre2.zip

Best to try it only in an environment that you aren't afraid to break, 
including Dom0 and any other DomU's on the system. That said, I am running this 
version on some semi-production DomU's without any issues.

James


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