Unresponsive VMs, backup from NVME-SSDs

Jun 5, 2023
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We have a Proxmox cluster with 2 storages:

- a ZFS with 2 NVME Enterprise SSDs
- a software RAID with LVM-Thin and 2 NVME Enterprise SSDs

In both cases, when backing up to the Proxmox backup server, the VM, as well as all other VMs on the system, become so slow that the VMs are no longer usable while the backup is running.

The disk scheduler is set to None, we also tried Deadline.
CPU is a 16 Core AMD EPYC.

Any suggestions, what could be causing this?