Ok, that was kinda premature and stupid panic.
#Beszel agent was not reporting Disk I/O until the recent update. All agents are updating automatically, and that happened just around March 28-30. After that, the data began to flow.
In fact, I have sudden disk issues only with a single #Proxmox node, and it is clearly visible on the IO pressure stall graph. Spikes before May 30 are backups. Then it went crazy.









