qm-rescan

Rescan all storages and update disk sizes and unused disk images of a specific virtual machine

$ qm rescan [vm_id]

$ qm rescan --dryrun [true] [vm_id]

qm rescan

VMID
    The ID of the virtual machine to rescan. This is a numerical identifier assigned to each VM within Proxmox VE.

The `qm-rescan` command is a utility used within Proxmox VE to trigger a rescan of QEMU virtual machine disks. This is particularly useful after making changes to the underlying storage, such as resizing logical volumes or adding new disks to a storage pool. Without a rescan, the Proxmox VE host might not be aware of these changes, leading to incorrect disk sizes being displayed or an inability to access newly added storage. This command essentially instructs QEMU to re-enumerate the disks attached to a particular VM, forcing it to recognize the updated disk geometry and any newly available storage. It ensures that the guest operating system within the virtual machine can properly utilize the modified storage, and Proxmox VE reflects the actual disk state. It avoids restarting the vm to get the correct sizes of the disks in the os.
It's a very important command for storage administration.

The command only rescans the disk configuration and does not modify the guest operating system in any way. The guest OS must still detect and use the added/resized storage by itself (e.g., by scanning for new disks or resizing partitions).

To rescan the disks of a virtual machine with ID 100, run:
`qm rescan 100`

If the rescan does not appear to be effective, ensure that the underlying storage changes have been properly applied (e.g., LVM resizing, ZFS pool expansion). Also, check the QEMU logs for any errors during the rescan process.
Sometimes the guest os does not have the correct drivers.

The `qm-rescan` command has evolved as a crucial part of Proxmox VE's storage management capabilities. Early versions of Proxmox VE often required restarting VMs to recognize changes in the underlying storage. The introduction of `qm-rescan` provided a more convenient and less disruptive way to update the virtual machine's disk configuration without incurring downtime. It's development was centered around improving efficiency and avoiding unnecessary VM reboots in dynamic storage environments.

qm(1), lvresize(8), pvresize(8), rescan-scsi-bus.sh(8)