Re: AW: KVM backup and snapshots

[Anthony Liguori <anthony@codemonkey.ws>]

Dietmar Maurer wrote:
>> like a 'savevm' without qcow2 requirements?
>>
>> would be great.
>>     
>
> Yes, something like:
>
> # savediff [filname] [maxsize]
>
> After a backup you can revert all changes, so you basically have a
> snapshot.
>   

Actually, I think a simple change to the 'change' monitor command would 
suffice.  If it were changed to allow non-ejectable block devices to be 
changed atomically, perhaps with a force flag, you could do the following:

qemu -hda foo.img

# create temporary qcow2 file that backs to foo.img
qemu-img create -f qcow2 -b foo.img tmp-hda.img

# in the monitor
(qemu) change -f ide0-hd tmp-hda.img
# do whatever you need with foo.img
(qemu) stop
(qemu) commit ide0-hd  # sync tmp-hda.img with foo.img
(qemu) change -f ide0-hd foo.img
(qemu) continue

obviously, if you script it, you'll minimize downtime.  We could get 
smarter and support a "live" commit that allowed a guest to keep running 
too which would make the downtime near-zero.

N.B. your base image can be anything, including an LVM partition.

Regards,

Anthony Liguori

> - Dietmar
>
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