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QCOW2 (QEMU Copy-On-Write) file format

.qcow2 · .qcow  ·  virtual disk image  ·  introduced 2008 by QEMU

What is a QCOW2 (QEMU Copy-On-Write) file?

QCOW2 (QEMU Copy-On-Write version 2) is the native virtual disk format of QEMU and the default for KVM-based clouds like OpenStack. It supports snapshots, internal compression, AES encryption, and copy-on-write backing files for cheap VM cloning.

Most readers reach this page after double-clicking a .qcow2 file and finding their operating system unsure what to do with it. The good news: QCOW2 (QEMU Copy-On-Write) is a well-understood format with mature tooling on every major platform. It is supported in one click by mainstream archivers on Windows, macOS, and Linux.

How to extract a QCOW2 (QEMU Copy-On-Write) file

Opening a .qcow2 file is straightforward on every modern operating system. The exact steps depend on which platform you are on:

On Windows

  1. Locate the .qcow2 file in File Explorer.
  2. Right-click the file. If you have 7-Zip installed, choose 7-Zip → Extract Here. On Windows 11 the built-in extractor handles ZIP, 7z, RAR and several other formats directly through Extract All…
  3. If prompted, pick a destination folder and click Extract.
  4. The extracted files appear in a folder next to the original archive.

On macOS

  1. Find the .qcow2 file in Finder.
  2. Install The Unarchiver from the Mac App Store, or Keka for both creating and extracting.
  3. Right-click the file → Open With → The Unarchiver (or just double-click after Unarchiver is set as the default).
  4. The extracted folder appears next to the archive.

On Linux

  1. Use your file manager: right-click the archive → Extract Here (file-roller on GNOME, Ark on KDE).
  2. On the command line, run one of: 
    7z x archive.qcow2    # works for almost any format
  3. The files appear in the current directory.

How to create a QCOW2 (QEMU Copy-On-Write) file

To pack files into a .qcow2 archive, you typically need an archiver that supports writing this format. Not every tool can create every format — for example, only WinRAR can create real RAR files. The sidebar lists the software known to read and write QCOW2 (QEMU Copy-On-Write).

On the command line, the canonical create command is:

# Use 7-Zip, PeaZip, or the format's reference tool to create .qcow2 files.

If you regularly create archives at scale, a dedicated archive automation suite can wrap this command in scheduled jobs, integrity checks, and offsite replication.

Strengths

  • Open and well-documented
  • Built-in snapshots
  • Optional zlib/zstd compression
  • Backing files for COW chains

Weaknesses and limitations

  • Slower than raw images
  • Less common on Windows hypervisors

Typical use cases

  • KVM/QEMU virtualization
  • OpenStack and Proxmox VMs
  • VM snapshots and clones

Technical details

QCOW2 (QEMU Copy-On-Write) uses the Sparse + zlib/zstd cluster compression algorithm and is identified on disk by the magic byte sequence QFI\xFB. The standard MIME type is application/octet-stream. The format is an open specification and is free for any use.

Frequently asked questions

Is QCOW2 (QEMU Copy-On-Write) safe to open?

Archive files are containers — they are only as safe as what they contain. A .qcow2 from a trusted source is fine; one received from a stranger can hold malicious executables, scripts, or files engineered to exploit bugs in your archiver. Always keep your archiver updated, and never run unknown executables that come out of an archive. A safe workflow is to extract into a sandbox and scan the contents before opening anything.

What is the maximum file size?

Modern implementations support archives in the multi-terabyte range. The practical limit is your filesystem (FAT32 caps at 4 GB; ext4, NTFS, APFS, and exFAT all comfortably handle multi-TB files).

Can I password-protect a QCOW2 (QEMU Copy-On-Write)?

Some archivers can wrap QCOW2 (QEMU Copy-On-Write) files in an encrypted container, but the format itself does not always include built-in encryption. Check your archiver's documentation.

How does QCOW2 (QEMU Copy-On-Write) compare to other formats?

See our format comparison pages such as ZIP vs 7z, ZIP vs RAR, and tar.gz vs tar.xz for side-by-side feature tables.

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