These commands will help you find disks that are not connected to any VM. You need to run it on the Proxmox node. Replace POOL_NAME with the name of your pool
for i in $(rbd ls POOL_NAME); do if ! grep -r "$i" /etc/pve/nodes/ > /dev/null; then echo POOL_NAME/$i; fi; done;
Be careful. Don't trust the script output 100%. Check every disk!!!
Example:
There are no such VMs:
Then run the command:
rbd rm YOUR_POOL_NAME/DISK_NAME
If the disk is protected from deletion, check the snapshots:
rbd snap ls YOUR_POOL_NAME/DISK_NAME
We need to remove the protection. In my case, the command looks like this:
rbd snap unprotect HDD/vm-102-disk-2@barcdaily191217100934