On Sun, Jan 14, 2007 at 02:06:38PM +0100, Goswin von Brederlow wrote:
> Ligesh <myself@xxxxxxxxxx> writes:
>
> > Sat, Jan 13, 2007 at 07:26:58AM +0530, Ligesh wrote:
> > On Sat, Jan 13, 2007 at 12:57:04AM +0800, Tim Post wrote:
> >> .. and incremental thereof, on a typical (classic) linux system.
> >>
> >> While I agree that lvm snapshots are the easiest way (now), if
> >> developing something better, shouldn't a smaller option come into play?
>
> I'm assuming you want to make a snapshot without shutting down the domU.
>
> The problem with lvm snapshots is that xen does not pass down the
> sync/suspend event from the dom0 to the domU. Normaly when you create
> a snapshot from a mounted filesystem the fs gets asked to get itself
> into a consistent state before freezing it. Not so with snapshoting in
> dom0 and the filesystem mounted in domU. As a consequence mounting the
> snapshot in dom0 can have filesystem errors, the mount can easily
> fail.
What I was proposing was a new option for xm, where it will be able to tell
the domU to sync and suspend. We just need a domU kernel that will cooperate
with this request. The problem with daemon is that a lot of checks and measures
has to be in place to make sure that everything has happened as we thought it
would, which in practice never happens anyway. If we can have a specific domU
kernel that's aware of this feature, then it would provide almost 100%
guaranteed consistency.
Thanks.
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