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

[Geert Janssens <info@xxxxxxxxxxxx>]

On Thursday 21 May 2009, Javier Guerra wrote:
> On Thu, May 21, 2009 at 10:32 AM, Geert Janssens <info@xxxxxxxxxxxx> wrote:
> > * The Guest machines are all configured to get their IP address via dhcp,
> > and each guest config has it's own unique MAC address. So each guest will
> > appear on their own ip address
> > * There is no data on the guest disk images (only OS and applications).
> > All variable data is accessible via samba shares. So I don't delete
> > anything valuable by overwriting a disk image with the new master.
>
> if there's no state on those images, you can mount them as readonly
> and use the same for all DomUs.  of course, any update means shutting
> down
>
I never tried this... Won't Windows complain if it's running off of a read 
only disk ? I suppose Windows is writing to temporary files, or is keeping 
state in it's registry. I'm not interested in these local state differences 
between guests, that's why I can simply replace one guest's disk with an 
updated master copy. But I just don't know if Windows can handle a readonly 
"C" drive.
As for shutting down, that's no problem. I can plan for maintenance downtime 
pretty easily. The guests aren't used fulltime.

> > It works ok, but I'm using a lot of wasted diskspace. I still intend to
> > try and setup an LVM based disk image and use LVM snapshots for each
> > guest. This would give me essentially the same thing but with less wasted
> > diskspace. The experiment will have to wait until I find some time for it
> > though.
>
> note that using snapshots and a 'master' (either LVM or qcow) means
> you can't change the 'master' and expect the snapshots to catch the
> updates
I'm well aware of that and I can live without this advanced feature. As I 
understand it from reading this list, ZFS is currently the only filesystem 
that has something along those lines. But I may even misunderstand that much.

Geert
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