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. > 2. I have seen that at times the qemu monitor command is not able to connnect > to the monitor socket as libvirt it seems controls the monitor socket. If I > shutdown libvirt then commands like socat is able to connect. But since my > current environment does use libvirt, shutting down libvirt is not an option. > Is there any way around this ? New versions of libvirt have a virsh "qemu-monitor-command" command you can use to send a QEMU monitor command. Stefan