QCOW Image Format

QEMU uses the QEMU Copy-On-Write (QCOW) files to store a disk image.

File signature

QCOW files start with hexadecimal: 0x51 0x46 0x49 0xfb (ASCII: "QFI.")

File types

Currently there two are versions of the QCOW format; version 1 and 2. Version 2 is the preferred format.

Contents

The QCOW format is used to store storage media data, e.g. disk images.

The QCOW image file consists of:

• the file header
• the L1 table (cluster aligned)
• the reference count table (cluster aligned)
• reference count blocks
• snapshot headers (8-byte aligned on cluster boundary)
• clusters containing:
  • L2 tables
  • storage media data

The clusters are 512 bytes of size

Encryption

The QCOW2 format supports optional AES encryption

External Links

• The QCOW Image Format
• The QCOW2 Image Format