Re: Spawn new domains from a snapshot.
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On 05/25/2012 07:48 AM, NoxDaFox wrote: > Hello everybody, > > I would like to be able to spawn several domains from a given snapshot. So would I. It's not yet possible from libvirt, but we are getting closer as we discuss ideas of how to do it. > > Here's a possible scenario: > - I start from disk image A.qcow2. > - I made some changes to A and I take different snapshots: 1 - 2 - 3 Disk snapshots, or full system checkpoint snapshots with VM state? > - While A is still running I would like to run domains B and C from snapshot 2 Do you want B and C starting from A's memory state (hard) or just from A's disk state (easier)? > I don't want to revert a domain, I want to create new ones. The > original should be still running but it may be stopped if necessary. > > The idea I had was to create a qcow2 image through qemu-img (let's > call it Z.qcow2), as I'm using copy on write for performances then I'd > need to commit the changes contained in Z to A always using qemu-img. > Is there any other better way? I would love to do it through libvirt, > maybe specifying in the config file the backing store path of the > whole disk and then giving as a source file the one containing deltas. It sounds like you want the following qcow2 hierarchy: A.base <- 1.snap <- 2.snap <- 3.snap \- B.snap As long as 2.snap is read-only for both A and B, then 3.snap (used by A) and B.snap (used by B) can safely diverge in contents. > > This could be a good idea for realizing a cloud based system as a > incredible amount of time would be saved though it. > Imagine moving only qcow2 file containing deltas through the network > and then give the base image to each node so that it can use it for > start it's own domain. Yes, thin provisioning via common base images is already part of VDSM management of clouds. > As well would be possible to store the heavy base image in a single > node saving storage space. > Lots of cpu cycles saved once new image versions must be deployed > (typical case a windows update to propagate in the nodes network). -- Eric Blake eblake@xxxxxxxxxx +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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