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Re: [Xen-users] Major corruption of Windows HVM disks - Xen 3.4

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Major corruption of Windows HVM disks - Xen 3.4
From: Adam Wilbraham <adam.wilbraham@xxxxxxxxxxxxxxxx>
Date: Mon, 08 Jun 2009 14:04:27 +0100
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On 08/06/09 13:49, James Harper wrote:
Have you established that the virtual disks are definitely corrupt, as
opposed to something gone wrong in Dom0 that makes them seem corrupt. I
can't think what would cause that situation to arise though.

The first thing I did was to try and bring up all 3 VMs on the host that they are replicated to using DRBD. This host is still using Xen 3.2.1 as I haven't upgraded it yet - I was waiting to see how things went before doing both.

Are you using my GPLPV drivers? If so, then I would really like to hear
more about what went wrong so I can look into it and make sure it isn't
a problem with the drivers, although for all 3 domU's to fail
simultaneously like that it would be unlikely to be a DomU side problem.

A couple of the VMs do have an older version of the GPLPV drivers on but they were not active - I experienced problems with live migration when using your drivers so had to stick with pure HVM. I will be trying them out again in the near future as they appear to have progressed well over the last number of months, but as I say they are currently disabled so I would be 99% sure that they aren't to blame.

In my experience, the qemu drivers are prone to this sort of thing on
unclean shutdowns unfortunately, although I would have thought less so
with 3.4 than with 3.2... I have seen it before under 3.1 with Dom0
running out of memory and firing up the OOM killer (snmpd memory leak),
although the worst I've seen was a corrupt Exchange database that
restored without further problems.

The corruption did seem pretty bad on all 3 but I am indeed thinking qemu may have been part of problem here. I'm just about to start trawling the logs to see if there is anything useful in there.

Did you upgrade the Dom0 kernel when you upgraded xen?

No - still using 2.6.18-6 which is a standard Debian Etch kernel. I contemplated moving to the custom compiled one but everything I read on the list suggested that the Etch one would be fine. Can you see any benefit in upgrading the dom0 kernel too? Like I say this entire system has been rock solid on 3.2.1 since it was built in late 2008. The only driver for upgrade was that it was running a 32bit hypervisor and we needed more memory - I just thought bringing the base platform up to date would be a good idea at the same time.

Good luck with the restores.

Thankfully everything is back up and running now - backups are a great thing when you actually take them!

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