Performance trouble with VM during backup

[sherminator]

Hi everybody,

for testing purposes I built up a fresh PVE node using the current ISO image.
Then I created a ZFS pool (zfspool1, 4 SSDs) for disk images.
One further SSD acts as a local backup storage - an XFS formatted partition is mounted to /backup and connected via "directory storage" to PVE.
Then I created a VM with two virtual disks (10 GB and 1 TB) located in zfspool1.

When I do "Backup now" (Storage: backup, Mode: snapshot, Compression: LZO: fast) backup starts as expected. After a short time strange things happen inside the VM:
Some processes come and go, using 100% CPU. For example:
kworker/...
migration/...
watchdog/...
vballoon
irqbalance
scsi_eh_...

Sometimes the VM is hardly reachable/usable, sometimes everything looks fine during backup.

Can anyone explain this behaviour? The backup process reads the virtual disks with about 900 MB/s. Are my disks too fast? ;-)

Thanks a lot and greets
Stephan

 

[sherminator]

no ideas?
Could anyone help me to understand how proxmox backup can have an impact inside a VM? Or any hints what can I do to debug this?

Thanks and greets
Stephan