Re: kvm virtualization, consistent guest backup
On Tue, Aug 17, 2010 at 03:49:05PM +0200, Glennie Vignarajah wrote:
> > well my question was about how to do it without guest shutdown.
>
> I am not aware of any software for doing this (ie backingup VM online with
> appplication level consistency).
>
> In order to minimize the downtime, you may try to save the state of the VM, do
> your LVM snapshot and restore the state. Have a look at virsh man page for
> more details.
> But I *don't* think is method will guarantee application/DB consistency!
Data consistency is a problem that has to be solved at the application level,
but what I need is a filesystem consistency. Snapshotting filesystem from host
mounted in the guest will leave it a mess. I need to do what lvm in the host
does, which is to tell the filesystem to get synced a frozen into a clean
state and then it probably is possible to make an lvm snapshot from the host
and get a consistent filesystem. I can synchronize database before the fs
freeze.
I know that the kernel can do that but I don't know how to force it from
userspace. lvm snapshot does it automaticaly.
Of course there might be other problems I'm unaware of. I think that online
backups is something that has to work for example in HA environment. You can
hardly provide HA but keep shutting down clusters for consistent backups. What
would otherwise be the point?
>From what I've heard, vmware is capable of backing up running guests so there
has to be a way.
mk
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