QCOW Image Format

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

MIME types

File signature

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

File types

Currently there are three versions of the QCOW1 format; namely QCOW (version 1) and QCOW2 (version 2). Version 3 is considered an extended variant of QCOW2.

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

See Also

External Links

Tools