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Re: [Xen-users] Windows XP HVM on qcow diskfile and snapshots

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Subject: Re: [Xen-users] Windows XP HVM on qcow diskfile and snapshots
From: Geert Janssens <info@xxxxxxxxxxxx>
Date: Wed, 15 Apr 2009 20:43:58 +0200
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On Saturday 11 April 2009, Fajar A. Nugraha wrote:
> On Sat, Apr 11, 2009 at 9:10 PM, Geert Janssens <info@xxxxxxxxxxxx> wrote:
> > Dom0: CentOS 5.2 i386, with gitco Xen 3.3.1 i386.
> ...
> Last time I check, tap:qcow does not work when using Windows with
> GPLPV or HVM Linux with PV drivers.
> The only other alternative that I know of, with acceptable performance
> and space allocation flexibility, is to bring in Opensolaris with zfs
> volume, either as dom0 or as iscsi server.
> Regards,
> Fajar

And on Sunday 12 April 2009, Brian Conway wrote:
> On Sat, 11 Apr 2009 16:10:21 +0200
> Geert Janssens <info@xxxxxxxxxxxx> wrote:
> > * Created a copy-on-write disk image, based on my original image with
> > qemu-img create -b <original image> -fmt qcow <new image>
> > and changed the blockdevice line in my config file to
> > disk = [ 'tap:qcow:<new image>,hda,w', ',hdc:cdrom,r' ]
> >
> > However, this configuration won't boot. To be exact, the guest aborts
> > very shortly after the bios hard drive discovery. So I presume the
> > copy-on-write disk image is somehow not working.
> >
> > Any hints on what goes wrong here ?
> I have the same problem with a freshly created qcow2 image using the
> qemu-img-xen tool.  The original qcow2 image works perfectly with
> tap:qcow2, but attempting to use it as a base for a new image halts the
> boot immediately.  The xend.log file don't show any errors, it only
> points me to the VM-specific log, which just stops dead.
> Perhaps this functionality isn't supported?
> Brian Conway

Thanks both Brian and Fajar for your replies.

Unfortunately, iscsi or zfs are no options for now.

But I am now considering another approach:
My dom0 runs lvm. So I might convert the qcow disk image to an lvm partition 
and use that as the block device for my XP domU.
LVM has got snapshotting capabilities as well. So I would have one base WinXP 
partition (like a base qcow disk image). The idea is to run updates first on a 
snapshot of this LVM, to check if there are no issues.

Of course this new idea comes with another set of questions:

1. Would such a setup make sense ?
2. What performance could I expect from the lvm based setup compared to qcow 
based disk images (better or worse indications suffice) ? Most of what I read 
on the list suggests that lvm should be faster.
3. Do the GPLV drivers work with an LVM based block device ? And also on a 
snapshot ?

Thank you,

Kobalt W.I.T.
Web & Information Technology
Brusselsesteenweg 152
1850 Grimbergen

Tel  : +32 479 339 655
Email: info@xxxxxxxxxxxx

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