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xen-users
Re: [Xen-users] GPLPV and LUN's on a storage
On Mon, Oct 26, 2009 at 03:29:03PM +0100, Klaus Steinberger wrote:
> Hi,
>
> just a information:
>
> I did run into big troubles running Windows HVM VM's with GPLPV driver on
> LUN's on a storage system. (In my case a CX4 from EMC).
>
>
> What happened:
>
> After e.g. Windows Updates the VM's rendered unbootable
>
>
> What causes this:
>
> My assumption is: Windows boots from the Qemu device until some point
> there it switches over from the QEMU device to the PV System device. But
> qemu uses the VM Caches from DOM0, but with the PV driver the LUN is
> accessed directly.
>
> Now it happens after a reboot that the VM caches are preloaded from
> previous boots, but the LUN contains really already different data. This
> leds to curious crashes.
>
>
> My solution to avoid that:
>
> Dropping caches with "echo 1 > /proc/sys/vm/drop_caches"
>
> This could also be added to the xm definition files, as they are just
> python:
>
> os.system('echo 1 >/proc/sys/vm/drop_caches');
>
>
>
> I already had a similar problem with paravirtualized linux VM's on a Redhat
> System and external LUN's. pygrub did show old boot entrys, different from
> what the VM has. Same reason. Dropping vm_caches in this case also helped.
> There is currently a bug open on redhat's Bug Tracker.
>
> Bug #466681
>
> They work on direct I/O for at least pygrub.
>
Do you use phy:, file: or tap:aio: ?
-- Pasi
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