Hi. I'm following here a conversation that was initiated on Kashyap's website [1]. We have a server we use as a host for virtual machines using KVM (virt-manager used for VM creation) and we would like to setup VM backups. Basically, we're thinking of a backup schedule like "keep 7 daily and 4 weekly backups". We'd rather not shutdown the VM every day so live backups would be nice. I've been doing my best with documentation found on the Internet. It is likely that the path I chose was not the best, so feel free to tell me if I'm asking the wrong questions and I should be proceeding totally differently. AFAIU, backups can be done at filesystem level (using LVM) and at virtualization level (using libvirt). We chose the libvirt way. AFAIU, live backups using libvirt may be done thanks to blockcommit as explained here on the wiki [2]. -> Considering our use case, is this the recommended way? Assuming yes, here is the plan. I wrote a script that does # Create snapshot virsh snapshot-create-as --domain $VM_NAME snap --diskspec vda,file=$VM_DIR/"$VM_NAME"-snap.qcow2 --disk-only --atomic --no-metadata --quiesce # Copy frozen backing file cp $VM_DIR/"$VM_NAME".qcow2 $SNAP_FILEPATH # Blockcommit snapshot back into backing file virsh blockcommit $VM_NAME vda --active --pivot # Remove snapshot file rm $VM_DIR/"$VM_NAME"-snap.qcow2 Variables should be self-explanatory: - VM_DIR is the directory where the VM are stored - VM_NAME is the name of the VM, and its qcow2 file is called VM_NAME.qcow2 - SNAP_FILEPATH is the full path (including name) where the backup should be created Using this scheme, we only keep snapshots for the time of the VM file copy, which is less than a minute. The backing chain is at most 'back <- snap', and most of the time just 'back'. If something ever happens to the VM (human error while being logged as root, attack from the internet,...), we'll turn off the VM, replace its qcow2 file and turn it back on. I understand that this method only saves disk states, so the VM will be started as if it had been powered-off suddenly while running (not quite: thanks to the '--quiesce' option, at least the disks are in a sane state). Not perfect but better than nothing. Those backups are meant to be used only when all else failed, anyway, it's not daily use. -> Does this make sense? Am I missing a feature or even a different approach that would make things simpler or more secure? Am I using libvirt snapshots for what they're not meant to? -> Anything wrong about my snapshot-create-as and blockcommit command lines? May I remove the snapshot with only a rm command? Now, a few side questions, as I might have messed up with the VM I was experimenting with. I used the same command lines as described above, except I didn't pass the '--no-metadata' option. Once the backing file was copied, I deleted the snapshot qcow2 file and thought I was done with it, until I realized the snapshot was still listed by virsh snapshot-list. And I couldn't find a way to delete it. (For the record, I asked on serverfault about that [3].) Ultimately, I found the snapshot's .xml descriptor and deleted it (in fact, moved it) while libvirtd was down. Now, the snapshot is not listed anymore. -> Am I getting away with it? Are there still some traces about that snapshot? Is my VM in an unsafe state? Anything I should do about it? -> What would be the proper way of dropping an external snapshot that was created without the '--no-metadata' option, then blockcommitted? I understand libvirt doesn't do it yet. Thanks for any hint. I naively thought our use case was pretty usual, and I must admit I didn't think I'd have to dive into this complexity, which is why I'm thinking there might be a more "common" way... [1] http://kashyapc.com/2014/10/07/libvirt-blockcommit-shorten-disk-image-chain-by-live-merging-the-current-active-disk-content [2] http://wiki.libvirt.org/page/Live-disk-backup-with-active-blockcommit [3] http://serverfault.com/questions/721216/delete-orphan-libvirt-snapshot -- Jérôme _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
