Remove orphan disks in Proxmox
If you canceled disk movement in Proxmox, an orphaned disk will be created. In such case, it will not be shown in VM hardware configuration, and it can not be removed from storage session. If you try to remove it, you will have an error as the disk is attached to a VM.
In order to remove it, rescan disk is required.
Rescan
Use following command can make the orphan disk reattached to the VM.
qm rescan --vmid <vm_id>
*Note: rescan should be done in the Proxmox node which contains VM configuration, otherwise, could not find the VM configuration file error will appear.
References
https://forum.proxmox.com/threads/cancelled-disk-move-orphaned-disk.96650/