Thank you Stefan, Jes. So it appears that snapshot_blkdev is the way to go for
vm disk backup with running vms.
In regard to merging changes, assuming that we go snapshot_blkdev rightaway.
Stefan's suggestion: "qemu-img commit"
Jes's suggestion: "qemu-img convert"
Does qemu-img convert apply to running VM's. In that case it would appear to be
the more practical approach(since vm shutdown would not be required).
Also incase If i have interpreted "qemu-img convert" incorrectly and does
require a VM shutdown. Then when is expected time when the "live merge" will be
available.
Thanks and Regards
Saurav Lahiri
--- On Fri, 11/3/11, Jes Sorensen <jes.soren...@redhat.com> wrote:
From: Jes Sorensen <jes.soren...@redhat.com>
Subject: Re: [Qemu-devel] Issue with snapshot outside qcow2 disk - qemu 0.14.0
To: "Stefan Hajnoczi" <stefa...@gmail.com>
Cc: "SAURAV LAHIRI" <saurav_lah...@yahoo.com>, qemu-devel@nongnu.org
Date: Friday, 11 March, 2011, 2:31
On 03/10/11 22:04, Stefan Hajnoczi wrote:
> On Thu, Mar 10, 2011 at 7:57 PM, SAURAV LAHIRI <saurav_lah...@yahoo.com>
> wrote:
>> The high level use case is that of being able to backup user specified disks
>> of a VM without having to bring down the VM.
>
> Excellent, that sounds exactly like Jes is addressing so future
> QEMU/KVM releases will hopefully have the live snapshot/merge
> capability.
>
>> snapshot_blkdev: Regarding this I do have a couple of questions.
>>
>> 1. If the snapshot cannot be merged then it could mean that there are
>> several snapshot files. One readonly for each of the previous snapshots and
>> the last one being the active one, which handles all the current writes.
>> Post backup If do have to restore to a particular snapshot then i would
>> probably have to copy all the files in the chain and maintain the entire
>> chain. But would it not affect read performance if several snapshot files
>> are maintained, particularly if the VM is hosting a database like mysql ?
>> Could you please clarify.
>
> If the VM is not running you can use the qemu-img commit command to
> merge the snapshot back down into the base image. After that you only
> have one image file again and can restart the VM. Hopefully the
> deltas are small enough that this process is quick.
>
> In the future a live merge command will take care of this and avoid
> the downtime.
Yep, qemu-img convert should be able to copy it into a single image so
you can delete the chain.
Cheers,
Jes
