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List:       netbsd-port-xen
Subject:    Re: Dealing with domUs state
From:       Jean-Yves Migeon <jeanyves.migeon () free ! fr>
Date:       2010-04-11 14:16:11
Message-ID: 4BC1D9AB.3060904 () free ! fr
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On 04/11/10 15:26, Joel Carnat wrote:
> Hello,
>
> I am running NetBSD 5.0_STABLE/amd64 with xenkernel33-3.3.1nb1.
> I have a Windows domU that I'd like to backup from times to times.
> In software like VMware or VirtualBox, there is a feature called
> "snapshots" which enables to save a full state (memory, disk...) of a
> VM. This is a really convinient way to test patches or software.
>
> The only method I found on nbsd/xen was to shutdown the domU, copy the
> disk image file and start the domU. When I want to go back to a previous
> state, I stop the domU, replace the disk image and start the domU.

Basically, snapshotting follows these criterias:
1 -bring/wait for the system to be in a coherent state
2 - save the state
3 - restore it

YMMV, I have not tested it with a HVM domU; snapshoting is a special 
case of save/restore cycle, in a rapid succession:
- xm save HVM domU
- snapshot the disk image (either through dd, lvm, or qcow - it all 
depends on the kind of block image you chose for your HVM domU)
- xm restore HVM domU

> Is there some "better" way to deal with domU snapshots ?
> Especially ways that would enable to have to domU stil running when
> backuping and/or restoring ?
>
> TIA,
> Jo
>
> PS: the domU is hosted on a local FFSv2 partition, with "log" enabled.

For HVM, see above; for PV guests, my branch (jym-xensuspend) contains 
the necessary stuff (steps would be exactly the same though: 
save/snapshot hd/restore), but it needs more testing before I merge it.

-- 
Jean-Yves Migeon
jeanyves.migeon@free.fr


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