No incremental mode for stopped VMs?

[carsten2]

I have a VM with 1 TB of data which is switched of. The PBS does not use the incremental mode but reads the whole 4 TB over and over again.

[CODE
INFO: Starting Backup of VM 106 (qemu)
INFO: Backup started at 2020-08-24 09:14:05
INFO: status = stopped
INFO: backup mode: stop
INFO: ionice priority: 7
INFO: VM Name: rs-sbs
INFO: include disk 'scsi0' 'data1:vm-106-disk-0' 195G
INFO: include disk 'scsi1' 'data1:vm-106-disk-1' 4T
INFO: creating Proxmox Backup Server archive 'vm/106/2020-08-24T07:14:05Z'
INFO: starting kvm to execute backup task
INFO: started backup task '4e32c598-dcf4-429f-ab71-aa13aa8ef242'
INFO: status: 0% (184.0 MiB of 4.1 TiB), duration 3, read: 61.3 MiB/s, write: 61.3 MiB/s
[/CODE]

 

[harry700]

I believe that incremental mode is only supported for running VMs. This decision was justified in a previous response found here: https://forum.proxmox.com/threads/backup-vm-pve-to-pbs-how-to-enable-incremental.72843/post-325682

The main reason is that when the VM is running it has full control over its storage, so we can tell for sure if something on the disk was changed or not. Once stopped, anything could theoretically happen to those VM disk images - so we play it safe and verify all of it. If we find a guaranteed sane way optimizing this, we may do so in the future, for now we wanted to play safe - backups are really important after all.

 

[carsten2]

A backup solution which is not able to incrementally backup in the safest mode possible, is really not a good solution. There should be a solution to this problem.

 

[t.lamprecht]

I believe that incremental mode is only supported for running VMs

Note that incremental mode is always enabled, but certain optimizations like the dirty-bitmap (called "fast incremental backup") tracking is only available for running VMs.
There are plans to improve this for certain areas, for further information see my reply: https://forum.proxmox.com/threads/backup-vm-pve-to-pbs-how-to-enable-incremental.72843/#post-333594 to the exact same reply carsten2 made here (please avoid spamming the same reply to multiple threads!)