QCOW Cheatsheet

QCOW = QEMU Copy On Write.

qcow is a file format for disk image files used by QEMU.

Why qcow? It only takes up as much disk space as the guest OS actually uses.

CLI

CLI: qemu-img

# Show image info
$ qemu-img info disk.qcow2

# Convert an existing qcow2 image to new format
$ qemu-img amend -o compat=1.1 disk.qcow2

# Create a virtual disk
$ qemu-img create -f qcow2 myDisk.qcow2 20G

QCOW1 vs QCOW2 vs QCOW3:

• QCOW1 and QCOW2 have two completely different driver implementations and the two versions actually are exposed as two different image formats ("qcow" and "qcow2") to the user.
• QCOW3 is strictly an extension of QCOW2, it keeps the fundamental structure unchanged. Internally, QEMU will have a single driver for both QCOW2 and QCOW3 images.
• compat=1.1 means it is using the new QCOW3 format, though the file may still be named .qcow2.

Off the shelf

Debian 12: https://cloud.debian.org/images/cloud/bookworm/latest/debian-12-generic-amd64.qcow2