[ovirt-users] Re: Can't remove snapshot

On Thu, Jun 3, 2021 at 8:47 PM Strahil Nikolov <hunter86_bg(a)yahoo.com&gt; wrote: > > Hey Nir, > > you said that the data in the snapshot changed ? > I always thought that snapshots are read-only. Indeed snapshot is ready only - until you start to delete it. This is why we mark the snapshot as illegal once delete snapshot was started. It works like this: 1. Before snapshot Snapshots: (none) Volumes: A (active) A is read-write volume, changing while the vm is running. 2. After snapshot Snapshot: snap1 (disk snapshot A) Volumes: A <- B (active) A is now read only image, will never change B is read-write, modified by the vm B backing file is A 2. Start delete snapshot 1 Snapshot: snap1 (disk snapshot A, illegal) Volumes: A <- B (active) On the host running the vm, we perform block commit job, copying data from B into A. When the job completes, A contains all data in B, and any new data written to the B is mirrored to A. 3. Pivoting to volume A When the block commit has completed, we switch to vm to use volume A instead of volume B. At this point the VM is writing again to volume A, and volume B is unused. Snapshot: snap1 (disk snapshot A, illegal) Volumes: A (active) <- B 4. Cleanup On engine side, snapshot 1 is deleted On the host, volume B is deactivated On the SPM host, volume B is deleted Snapshot: (none) Volumes: A (active) I hope this is more clear now. Nir