qcow2-external-data-file · shipping · also QCOW2 data file

QCOW2 external data file

A QCOW2 external data file stores guest payload separately from the QCOW2 file that holds its mapping metadata.

Role: an external data file is different from a backing image that supplies inherited regions. A disk can require external payload storage without having a backing file. [1]

Interpretation: with data_file_raw off, a zero-cluster mapping can hide old payload bytes that remain visible when the external file is read directly. Raw mode on makes zero writes maintain the corresponding raw-file content, but does not authenticate later edits. [2]

Recovery: preserve the resolved data child and effective opening configuration, not only the stored name. Hesela's 60 offline observations include a runtime override that changes guest bytes while both original file hashes stay unchanged. Outcomes are scoped to the recorded QEMU package. [3]

Relations

related

QCOW2, QCOW2 backing chain, Backup verification

Citations

1. QEMU v8.2.2: external-data feature bits and standard cluster descriptors (accessed 2026-10-21)
2. QEMU v8.2.2 iotest 244: external data, zero writes and raw-mode controls (accessed 2026-10-21)
3. Hesela: QCOW2 external-data observations (accessed 2026-10-21)

JSON: /data/terms/qcow2-external-data-file.json