[CentOS-virt] using an lvm for kvm vm
incoming-centos at rjl.com
Sun Feb 13 20:14:02 EST 2011
On 02/13/2011 02:30 PM, Nataraj wrote:
> On 02/13/2011 10:21 AM, Dennis Jacobfeuerborn wrote:
>>> Could you then pause the virtual machine and safely take an LVM
>>> snapshot, continue the VM and then mount the snapshot on the host and do
>>> a backup?
>> Probably not. If you pause the guest then the filesystem on it might be in
>> an inconsistent state. You will be able to make a snapshot since that
>> happens on the block level but you might have problems mounting it.
> I've heard of somebody doing something to make this work. I think you
> could create another LV (from inside the VM - assuming a linux VM) on
> top of whatever raw partition was available to the VM. Then you could
> take the snapshot within the VM (which I believe guarantees that the
> filesystem is sync'ed when the snapshot is taken.) Then you use losetup
> and lvscan to make the lvm vg available on the host and I think you
> could access the snapshot without even pausing the vm.
I guess this is not the case. You can attach the VM virtual disk to the
loopback and see the VG and it's LV's, but they show up as unavailable.
I guess changing the snapshot to be available would be writing to the LV
structure and could cause corruption while the vm is running, so better not.
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