[SOLVED] High IO wait during backups after upgrading to Proxmox 7

In Proxmox VE 7.3, it's possible to configure the number of workers used for VMs for vzdump/backup jobs. It's not yet exposed via UI, please see this post for how to configure it.
 
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I also changed it to 1, as my small Atom CPU can't handle all the hashing/encryption/compression of PBS + ZFS overhead. Will report back after the next weekly backup, if it help when using weak CPUs. Average load jumping from 4 to 32 wasn't great when doing PBS backups and just using a weak quadcore CPU.
 
It is also necessary to restart or live migrate the virtual servers so they use the updated kvm binary.
max-workers=1 seems to be working well so far.

On one node I restarted some, but not all VMs
In this IO wait graph the arrows are when vzdump began on a VM running the updated KVM, the spikes in IO wait are backups of VMs still running on the old KVM binary.
1669991852159.png
 

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