Re: [Xen-users] Do xen support differencing disk image?

["Wenchao Cui" <cuiwc@xxxxxxxxxxx>]

Thanks for the info, Mats.

Regards.
Barney

On 6/26/07, Petersson, Mats <Mats.Petersson@xxxxxxx> wrote:

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Barney
> Sent: 26 June 2007 06:22
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Do xen support differencing disk image?
>
> Hi,
>
> As in Microsoft Virtual PC and VMware, differencing disk
> images are supported to enable snapshots and branches of
> virtual machine, do xen support these features? If the answer
> is yes, how to implement a differencing disk image?

There is a "snapshot" variable in the config options, but I don't know
if it works as I've never used it. Nor do I know exactly HOW it's meant
to work (aside from if you set it to zero it's off, and if you set it to
one [or any non-zero value, I expect] it's on).

A quick "grep" through the sources seem to indicate that this is only
available for HVM-mode where qemu-dm is used for the disk-access, but I
can't say absolutely for sure, as it may be more complicated than that.
[The "snapshot" variable is stored in the xenstore, so it may be that
the blkback driver is reasing xenstore and deciding to do things
"differently" when it's got the snapshot setting].

--
Mats
>
> Thanks.
>
> Regards.
> Barney
>
>
>

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