Background
LVM-Thin is great because you don’t use all the disk space and can share between hosts. However, it’s dangerous to oversubscribe if one of your users starts filling up their disk and you haven’t observed the warnings. Proxmox tries to warning you, but you’ll have to take manual (or script) action yourself. These warnings will look similar to the following:
iscsiadm: No session found. create full clone of drive scsi0 (nasX:base-9401-disk-0/vm-987-disk-0) WARNING: You have not turned on protection against thin pools running out of space. WARNING: Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full. Logical volume "vm-987-disk-0" created. WARNING: Sum of all thin volume sizes (11.73 TiB) exceeds the size of thin pool pve/data and the amount of free space in volume group (<16.38 GiB). drive mirror is starting for drive-scsi0 drive-scsi0: transferred 0.0 B of 130.0 GiB (0.00%) in 0s drive-scsi0: transferred 279.0 MiB of 130.0 GiB (0.21%) in 1s drive-scsi0: transferred 361.0 MiB of 130.0 GiB (0.27%) in 2s drive-scsi0: transferred 413.0 MiB of 130.0 GiB (0.31%) in 3s
So that begs the question. What exactly does this mean?
Set activation/thin_pool_autoextend_threshold below 100 to trigger automatic extension of thin pools before they get full.
Also, where do you set it?
It turns out you can’t set it and close monitoring of disk space is the best action:
How to monitor LVM-thin over provisioning on a Proxmox Host
At per the forum post, here is a good way to see real disk space in use. The command below will report values where actual space in use is > 70%:
pvesm status | grep lvmthin | awk ' $7 >=70 {print $1,$7}'