Disk image file saved in the second version of the QEMU Copy On Write (QCOW2) format, a format used by QEMU virtualization software; stores the hard drive contents of a virtual machine; similar to the .QCOW extension which is saved in the QCOW format; features a different strategy for storing multiple snapshots of the virtual machine.

QEMU’s disk allocation strategy allows for smaller file sizes because it delays allocation of storage until the disk space is needed. This differs from other policies that allocate fixed amounts of space, in which case some of the empty space may go unused. NOTE: The QCOW2 format replaced the QCOW format and, subsequently, the QCOW extension. However, QEMU is still compatible with disk image files saved in the original QCOW format.