2009/12/28 Pasi Kärkkäinen <[email protected]>

> On Mon, Dec 28, 2009 at 03:51:59PM +0000, John Haxby wrote:
> >    2009/12/28 J Newbie <[1][email protected]>
> >
> >      Btw, any other recommendation for backing up virtual machines.
> >
> [snip client-hosted backup]
> >
>
> We'd really need something like Windows VSS, to be able to coordinate
> the disk snapshots with the apps running in the guest..
>
>
That is possible and you don't need any especial software to do it.   At
least I didn't, not quite anyway.

I had a shell script that put the applications I was interested in into a
"safe" state -- depending on the application this was either a suspend or
just shutting it down (sendmail, for that one) -- did a sync and the
reported back to the host that the guest was ready for a snapshot.  When the
snapshot had been taken the applications were either allowed to continue or
restarted as necessary.

This isn't perfect: the guest file systems are still marked dirty, but the
sync ensures (I hope) that all the data is recoverable.

Getting clean file systems would require a change to the kernel so that all
disk activity is stopped and the various file systems are briefly marked
clean while the snapshot is taken.   I don't know if anyone, anywhere, is
looking at that.

jch
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