First of all, I'd like to thank you all for the very detailed replies. Even if I've learnt a lot today about libvirt snapshot features, I'm stuck because I'm currently using Ubuntu Precise which is very "conservative" about libvirt/qemu/kvm versions. :) I'll soon create a new hypervisor for testing purpose and I'll experiment the features/patches you've pointed out. Cheers, Davide. On 25/ott/2012, at 06:26, Kashyap Chamarthy <kchamart@xxxxxxxxxx> wrote: > On 10/25/2012 03:14 AM, Eric Blake wrote: >> On 10/24/2012 03:01 PM, Davide Guerri wrote: >>> Thank you Eric for the quick reply! >>> Do you know if there's a way to remove (not revert) an external snapshot on >>> a live domain? >> >> Depends on what version of libvirt and qemu you are using :) >> >> Qemu 1.2 and libvirt 0.9.10 provide the virDomainBlockRebase (qemu >> 'block-stream') for flattening an external snapshot chain by pulling >> into the active image, while the guest is running. You have to deal >> with the fact that every time you take a snapshot, the active image name >> changes, but it's fairly reliably as a way of reducing the impact of a >> long chain of external snapshots. >> >> Qemu 1.3 (due in December) will be adding a new 'block-commit' monitor >> command, which libvirt 1.0.0 (due next week) will also be able to reduce >> backing chains by committing data from a snapshot back into the backing >> image, while the guest is running. As of now, qemu.git is limited to >> committing just read-only portions of the backing chain, but we hope to >> expand that to also committing the read-write active layer of the chain. >> >> You can pair these chain-shortening commands with 'virsh snapshot-delete >> $dom $snapname --metadata' to make it appear as if the snapshot never >> happened. It is even possible to do a sequence of snapshots and >> pulls/commits to get back to the original file name (of course, with >> twice the work as you go through a temporary file name). > > > Just expanding on Eric's very lucid detail. > > David, here's some examples I posted with 'blockcommit' & 'blockpull'(with QEMU git & > Libvirt git as of 21st OCT) -- > > - http://kashyapc.fedorapeople.org/virt/blockcommit/recursive-blockcommit-base-raw.txt > - http://kashyapc.fedorapeople.org/virt/blockpull/test-blockpull.txt > > > Hope that helps. > >> >>> >>> I'm trying to backup (live) machines with the shortest downtime possible. >> >> Then you may also be interested in Peter's and my recent patches, which >> make it possible to back up machine RAM state in addition to disk state, >> with very minimal downtime, and which also enhance what you can do with >> revert and delete of those snapshots: >> https://www.redhat.com/archives/libvir-list/2012-October/msg01290.html >> It's definitely faster than the current downtime of 'virsh >> snapshot-create' without --disk-only, which can take seconds or even >> minutes where the guest is paused. >> >> Since Peter posted his series after the 1.0.0 freeze, I'm not quite sure >> whether we will take his patches this late in the release cycle, or if >> it will be another month (and 1.0.1) before they are available. >> >> You may also be interested in qemu 1.3 adding the 'drive-mirror' >> command, which allows for taking a copy of a disk ('virsh blockcopy') >> without affecting the backing chain in the first place. >> >>> >>> The script I'm using makes a (full) snapshot of a VM, restore its state, >>> copies (with qemu-img convert) the snapshot out of the qcow file and >>> removes the snapshot. >> >> So you want to convert back to raw? 'blockpull' can't do that, but >> 'blockcommit' (if it gains support for committing the active layer) and >> 'blockcopy' will be able to do so. >> >> Oh, and if you want an early preview of 'blockcopy', check out RHEV 3.0, >> where the qemu-kvm and libvirt versions as patched by Red Hat have >> already been using an early backport of the blockcopy code for several >> months now. >> >> >> >> _______________________________________________ >> libvirt-users mailing list >> libvirt-users@xxxxxxxxxx >> https://www.redhat.com/mailman/listinfo/libvirt-users >> > > > -- > /kashyap _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
