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
