Freeze during backup

shyrwall

New Member
Feb 22, 2026
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Hi

I have an odd bug that I wonder if someone has seen before and/or has a solution to.

I have a simple setup at home with Proxmox 9 with a few VMs. Storage is local ZFS mirror on SSDS and an NFS-mounted NAS for vm-backups.

One of the VMs is a nested Proxmox-instance with barely any usage. No mentionable i/o and 7% average CPU usage.

Now here's the odd part.

Every time I perform a backup on another VM, _not_ the nested Proxmox, the nested Proxmox freezes until the backup is done. CPU on the nested Proxmox shoots through the roof with the kvm process at 400% (4 cores at 100%) and I/O on it goes up to 20MB/s reads.

Also the backup is done to the NFS NAS and not to the SSDs where all the VMs are running.

Normally the backup is ~200MB/s to the NAS but even if I ratelimit it to 10MB/s the nested Proxmox still freezes until the backup is done.

I'm clueless

Thank you.