VM not responding during Backup

[Jackobli]

We are seeing applications / vms not responding during backup.
We assume, that this is in between the "fs-freeze" and "fs-thaw"?
How could we minimize this time or avoid the issue?

Setting:

• Cluster with 6 physical servers (only four are have vms to back up at the moment), Network is 25 GbE SFP28
• Filesystem is Ceph (mostly ssd, some vm also capacity rotating disks with ssd as cache)
• Backup server is Proxmox Backup Server (on 2 x 1 GbE, not saturated)

today (sample size just one day) we are seeing on 13 vm following times for freeze/thaw

• 2 x 0
• 3 x 1 sec
• 2 x 3 sec
• 2 x 4 sec
• 1 x 12 sec
• 3 x 14 sec