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Re: [Xen-users] is save and restore save?

To: Julian Hagenauer <chaosbringer@xxxxxx>
Subject: Re: [Xen-users] is save and restore save?
From: Harald Kubota <hkubota@xxxxxxx>
Date: Sun, 10 Sep 2006 11:18:43 +0900
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Julian Hagenauer wrote:
xm create myvm
xm save myvm state.dat
xm create myvm
(now logging on an do some modifikations)
xm destroy myvm
xm restore state.dat

Will that leave the filesystem consistent? Do i have a filesystem that is the 
same like the one at the point of the saving?
Is there a way to take a snapshot of a virtual machine for later staterestoring 
instead of shuting the machine down and copying its imagefile?

I thought about the same too and my conclusion was:

Since 'xm save' saves the memory and the state of the machine, but not the disk, any changes on the disk
and on swap space is bad.

However, if you do 'xm save', then do a snapshot from disks (including swap), then 'xm create' again (which will have an unclean filesystem just like after a crash), then 'xm destroy' and then undo all the recent changes on disk and swap (undo snapshot), THEN you can 'xm restore' that state again. Since memory is in the state.dat, and disk is unchanged (curtesy of lvm snapshots), that's ok.

That is, if lvm snapshots work as expected.

From what I gather on the web and several mailing lists, it's still marked as 'experimental' for a reason.

If you happen to have fancy hardware which can do snapshots in a reliable way, I see no problem.


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