This is really helpful, thanks. > The disk quiescing is not part of the backup operation and needs to be > done manually via 'virsh domfsfreeze' if required. The original
I assume quiescing *would* be necessary for workloads like databases and if we can live with a crash-consistent backup then we can bypass this, but if I was to include this, the sequence would be: virsh domfsfreeze <domain-name> virsh backup-begin <domain-name> virsh domfsthaw <domain-name> Again, I assume the qemu-agent would need to be running on the guest to allow freeze/thaw. I was about to ask how backup-begin is different from creating a disk-only, no-metadata snapshot but I think it is equivalent - the advantage is that we don't need to deal with merging the overlay file and pivoting afterwards, is that right? I also realised this is very like the sequence described at the bottom of that domainstatecapture page comparing 'direct backup' and 'Backup via temporary snapshot' - what confused me there and which I still don't understand are the two references to events. For direct backup, this step is: - wait for push mode event, or pull data over NBD # most time spent here Can you expand this any? I am assuming direct backup is a 'push' mode backup as per the description at https://libvirt.org/kbase/live_full_disk_backup.html - what is this push mode event? > By default a full backup creates a stand-alone image. If you'd use > incremental backups, then it is actually creating images that depend on > each other. OK, and that would be by populating an appropriate xml as per https://libvirt.org/formatbackup.html - which I think you answered on this list a year or two ago. > Yes it is. Note though that since the VM was likely running at the point > when you took the backup the 'restore' operation will look like a > cold-boot after a power failure at the exact time when the backup was > taken. > > > Snapshots also allow you to capture memory state and also pre-date > backups thus they are documented a bit more in depth. OK - just to make this explicit - if we want to capture memory state as well as disk then we *must* use snapshots, either internal or external? And - last question! - while we are covering the bases... managedsave sounds like it is designed for preserving a one-off recovery position for a potentially relatively long outage such as a hypervisor restart. VM restart will pick up just this latest saved image, but it *will* capture memory also? Once again thanks for your clarifications - it's clearing up a lot of confusion for me.
