Qcow

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qcow is a file format for disk image files used by QEMU, a hosted virtual machine monitor.^[1] It stands for "QEMU Copy On Write" and uses a disk storage optimization strategy that delays allocation of storage until it is actually needed. Files in qcow format can contain a variety of disk images which are generally associated with specific guest operating systems. Three versions of the format exist: qcow, qcow2 and qcow3^[2] which use the .qcow, .qcow2 and .qcow3 file extensions, respectively.

qemu-img command allows to inspect, check, create, convert, resize and take snapshot of qcow images.^[3] The e2fsprogs command e2image also has support for generating qcow2 files to avoid the use of sparse file support.^[4]