PBE 4.1 and VM snapshots

R

rbremer

New Member
Feb 27, 2026
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Our environment consist of Proxmox BE 4.1 running in a VE 9.1 cluster. All our VMs are thick provisioned in QEmu format, hosted on shared FC LUNs (LVM thick). The feature "snapshot as volume chain" is enabled for the storage LVs.

During a backup job the QemuAgent gets called to freeze the system. Some seconds later the agent is called again to resume disk i/o. All as expected. However, I am unsure on why I won't see any snapshot being taken of the VM during the backup. I do see CBT in action (in the backup log), but the VM doesn't show any snapshot being taken. Is this the expected behavior? Is the begin of the CBT based backup an "automatic, internal" snapshot, which is just not visible in the VE?

I need to ensure file system consistent backups and coming from a VMware environment I was expecting to see a snapshot being taken during backup.

Thank you for your advice.
 
Sure. I did two manual backups (mode snapshot) back to back:

Code: 
vzdump 135 --storage pbs-1 --remove 0 --mode snapshot --notification-mode notification-system --node node04 --notes-template '{{guestname}}'


135: 2026-02-27 17:59:22 INFO: Starting Backup of VM 135 (qemu)
135: 2026-02-27 17:59:22 INFO: status = running
135: 2026-02-27 17:59:22 INFO: VM Name: wsv19-01
135: 2026-02-27 17:59:22 INFO: include disk 'scsi0' 'Prod1:vm-135-disk-0.qcow2' 60G
135: 2026-02-27 17:59:22 INFO: backup mode: snapshot
135: 2026-02-27 17:59:22 INFO: ionice priority: 7
135: 2026-02-27 17:59:22 INFO: pending configuration changes found (not included into backup)
135: 2026-02-27 17:59:22 INFO: creating Proxmox Backup Server archive 'vm/135/2026-02-27T16:59:22Z'
135: 2026-02-27 17:59:22 INFO: issuing guest-agent 'fs-freeze' command
135: 2026-02-27 17:59:27 INFO: issuing guest-agent 'fs-thaw' command
135: 2026-02-27 17:59:30 INFO: started backup task 'f7e7719e-5dd8-4613-8b9b-cba22d2d12b9'
135: 2026-02-27 17:59:30 INFO: resuming VM again
135: 2026-02-27 17:59:30 INFO: scsi0: dirty-bitmap status: OK (8.7 GiB of 60.0 GiB dirty)
135: 2026-02-27 17:59:30 INFO: using fast incremental mode (dirty-bitmap), 8.7 GiB dirty of 60.0 GiB total
135: 2026-02-27 17:59:33 INFO:   9% (892.0 MiB of 8.7 GiB) in 3s, read: 297.3 MiB/s, write: 290.7 MiB/s
135: 2026-02-27 17:59:36 INFO:  14% (1.3 GiB of 8.7 GiB) in 6s, read: 141.3 MiB/s, write: 138.7 MiB/s
135: 2026-02-27 17:59:39 INFO:  17% (1.6 GiB of 8.7 GiB) in 9s, read: 92.0 MiB/s, write: 85.3 MiB/s
135: 2026-02-27 17:59:42 INFO:  22% (2.0 GiB of 8.7 GiB) in 12s, read: 142.7 MiB/s, write: 140.0 MiB/s
135: 2026-02-27 17:59:45 INFO:  27% (2.4 GiB of 8.7 GiB) in 15s, read: 145.3 MiB/s, write: 145.3 MiB/s
135: 2026-02-27 17:59:48 INFO:  30% (2.7 GiB of 8.7 GiB) in 18s, read: 88.0 MiB/s, write: 88.0 MiB/s
135: 2026-02-27 17:59:51 INFO:  35% (3.1 GiB of 8.7 GiB) in 21s, read: 154.7 MiB/s, write: 153.3 MiB/s
135: 2026-02-27 17:59:54 INFO:  37% (3.3 GiB of 8.7 GiB) in 24s, read: 65.3 MiB/s, write: 65.3 MiB/s
135: 2026-02-27 17:59:57 INFO:  41% (3.6 GiB of 8.7 GiB) in 27s, read: 110.7 MiB/s, write: 110.7 MiB/s
135: 2026-02-27 18:00:00 INFO:  44% (3.9 GiB of 8.7 GiB) in 30s, read: 90.7 MiB/s, write: 90.7 MiB/s
135: 2026-02-27 18:00:03 INFO:  46% (4.1 GiB of 8.7 GiB) in 33s, read: 61.3 MiB/s, write: 61.3 MiB/s
135: 2026-02-27 18:00:06 INFO:  48% (4.2 GiB of 8.7 GiB) in 36s, read: 42.7 MiB/s, write: 40.0 MiB/s
135: 2026-02-27 18:00:09 INFO:  50% (4.4 GiB of 8.7 GiB) in 39s, read: 80.0 MiB/s, write: 78.7 MiB/s
135: 2026-02-27 18:00:12 INFO:  52% (4.6 GiB of 8.7 GiB) in 42s, read: 58.7 MiB/s, write: 57.3 MiB/s
135: 2026-02-27 18:00:16 INFO:  54% (4.8 GiB of 8.7 GiB) in 46s, read: 40.0 MiB/s, write: 39.0 MiB/s
135: 2026-02-27 18:00:19 INFO:  59% (5.2 GiB of 8.7 GiB) in 49s, read: 160.0 MiB/s, write: 158.7 MiB/s
135: 2026-02-27 18:00:22 INFO:  63% (5.5 GiB of 8.7 GiB) in 52s, read: 102.7 MiB/s, write: 98.7 MiB/s
135: 2026-02-27 18:00:25 INFO:  64% (5.6 GiB of 8.7 GiB) in 55s, read: 29.3 MiB/s, write: 22.7 MiB/s
135: 2026-02-27 18:00:43 INFO:  65% (5.7 GiB of 8.7 GiB) in 1m 13s, read: 4.2 MiB/s, write: 4.2 MiB/s
135: 2026-02-27 18:00:46 INFO:  67% (5.9 GiB of 8.7 GiB) in 1m 16s, read: 85.3 MiB/s, write: 85.3 MiB/s
135: 2026-02-27 18:00:49 INFO:  69% (6.1 GiB of 8.7 GiB) in 1m 19s, read: 60.0 MiB/s, write: 60.0 MiB/s
135: 2026-02-27 18:00:52 INFO:  72% (6.4 GiB of 8.7 GiB) in 1m 22s, read: 85.3 MiB/s, write: 85.3 MiB/s
135: 2026-02-27 18:00:55 INFO:  74% (6.5 GiB of 8.7 GiB) in 1m 25s, read: 61.3 MiB/s, write: 61.3 MiB/s
135: 2026-02-27 18:00:58 INFO:  76% (6.7 GiB of 8.7 GiB) in 1m 28s, read: 60.0 MiB/s, write: 60.0 MiB/s
135: 2026-02-27 18:01:01 INFO:  80% (7.0 GiB of 8.7 GiB) in 1m 31s, read: 110.7 MiB/s, write: 109.3 MiB/s
135: 2026-02-27 18:01:04 INFO:  82% (7.2 GiB of 8.7 GiB) in 1m 34s, read: 52.0 MiB/s, write: 52.0 MiB/s
135: 2026-02-27 18:01:09 INFO:  83% (7.3 GiB of 8.7 GiB) in 1m 39s, read: 15.2 MiB/s, write: 15.2 MiB/s
135: 2026-02-27 18:01:12 INFO:  87% (7.7 GiB of 8.7 GiB) in 1m 42s, read: 140.0 MiB/s, write: 140.0 MiB/s
135: 2026-02-27 18:01:15 INFO:  91% (8.0 GiB of 8.7 GiB) in 1m 45s, read: 97.3 MiB/s, write: 97.3 MiB/s
135: 2026-02-27 18:01:18 INFO:  95% (8.3 GiB of 8.7 GiB) in 1m 48s, read: 117.3 MiB/s, write: 117.3 MiB/s
135: 2026-02-27 18:01:21 INFO:  96% (8.4 GiB of 8.7 GiB) in 1m 51s, read: 30.7 MiB/s, write: 30.7 MiB/s
135: 2026-02-27 18:01:26 INFO:  97% (8.5 GiB of 8.7 GiB) in 1m 56s, read: 28.0 MiB/s, write: 27.2 MiB/s
135: 2026-02-27 18:01:29 INFO: 100% (8.7 GiB of 8.7 GiB) in 1m 59s, read: 69.3 MiB/s, write: 69.3 MiB/s
135: 2026-02-27 18:01:55 INFO: backup was done incrementally, reused 51.38 GiB (85%)
135: 2026-02-27 18:01:55 INFO: transferred 8.74 GiB in 145 seconds (61.7 MiB/s)
135: 2026-02-27 18:01:55 INFO: adding notes to backup
135: 2026-02-27 18:01:56 INFO: Finished Backup of VM 135 (00:02:34)

Code: 
vzdump 135 --storage pbs-1 --remove 0 --mode snapshot --notification-mode notification-system --node node04 --notes-template '{{guestname}}'


135: 2026-02-27 18:02:17 INFO: Starting Backup of VM 135 (qemu)
135: 2026-02-27 18:02:17 INFO: status = running
135: 2026-02-27 18:02:17 INFO: VM Name: wsv19-01
135: 2026-02-27 18:02:17 INFO: include disk 'scsi0' 'Prod1:vm-135-disk-0.qcow2' 60G
135: 2026-02-27 18:02:17 INFO: backup mode: snapshot
135: 2026-02-27 18:02:17 INFO: ionice priority: 7
135: 2026-02-27 18:02:17 INFO: pending configuration changes found (not included into backup)
135: 2026-02-27 18:02:17 INFO: creating Proxmox Backup Server archive 'vm/135/2026-02-27T17:02:17Z'
135: 2026-02-27 18:02:17 INFO: issuing guest-agent 'fs-freeze' command
135: 2026-02-27 18:02:21 INFO: issuing guest-agent 'fs-thaw' command
135: 2026-02-27 18:02:24 INFO: started backup task '9ccdb7ef-ddbc-442f-a5df-c8a895e095a8'
135: 2026-02-27 18:02:24 INFO: resuming VM again
135: 2026-02-27 18:02:24 INFO: scsi0: dirty-bitmap status: OK (436.0 MiB of 60.0 GiB dirty)
135: 2026-02-27 18:02:24 INFO: using fast incremental mode (dirty-bitmap), 436.0 MiB dirty of 60.0 GiB total
135: 2026-02-27 18:02:27 INFO: 100% (436.0 MiB of 436.0 MiB) in 3s, read: 145.3 MiB/s, write: 144.0 MiB/s
135: 2026-02-27 18:02:27 INFO: Waiting for server to finish backup validation...
135: 2026-02-27 18:02:31 INFO: backup was done incrementally, reused 59.58 GiB (99%)
135: 2026-02-27 18:02:31 INFO: transferred 436.00 MiB in 7 seconds (62.3 MiB/s)
135: 2026-02-27 18:02:31 INFO: adding notes to backup
135: 2026-02-27 18:02:31 INFO: Finished Backup of VM 135 (00:00:14)
 
Code: 
why I won't see any snapshot being taken of the VM during the backup

As far as i know, for backups qemu creates it's own "snapshot", there are no snapshots created on the storage / file system itself.

Code: 
snapshot as volume chain

That's for manually created snapshots, qemu does not use / need this at all for backups.
 
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