Sunday, 11 December 2011


qcow stands for "QEMU Copy On Write" and denotes a deejay accumulator access action that delays allocation of accumulator until it is absolutely needed. QEMU is an adversary and basic apparatus container, and it can use a array of basic deejay images which are about associated with specific guests operating systems. The set of accessible deejay angel formats accept frequently accustomed abbreviate names:

vvfat - Basic VFAT

vpc - Windows Basic PC

bochs - Bochs book system

dmg - Macintosh deejay image

cloop - Linux aeroembolism loop

vmdk - VMware basic apparatus deejay format

qcow - QEMU Copy-on-write

qcow2 - QEMU Copy-on-write (new in adaptation 0.9)

raw - Raw book arrangement (no appropriate format)

cow - User-mode Linux copy-on-write


qcow images abound as abstracts is added, and abutment AES encryption or cellophane decompression.

One disadvantage of qcow images is that they can NOT be army with offset, in the way that raw images can be army with arise /path/to/image.img /mount/path -o loop,offset=32256.

qcow has been replaced by qcow2, but qemu and xen accept retained the architecture for backwards compatibility, and users should accede converting deejay images to qcow2 with


qcow2 is a newer adaptation of the qcow copy-on-write format. QEMU can use a abject angel which is read-only, and abundance all writes to the qcow2 image. Among the QEMU accurate formats, this is the best able format. Use it to accept abate images (useful if your filesystem does not abutment holes, for archetype on FAT32), alternative AES encryption, zlib based compression and abutment of assorted VM snapshots.

Mounting qcow2 images

For various reasons it might be useful to mount the disk image inside the qcow2 file, such as to edit configurations before starting the virtual machine, or simply to recover files from a backup. Since the qcow2 format is not a simple linear block format like disks and raw files, it is necessary to use the network block device tool that's part of the qemu toolkit like this: