hesela.devQCOW2
QCOW2 is a virtual disk image format that maps guest clusters to stored data, explicit zeros or data inherited from a backing file.
Mapping: guest-visible capacity and host file allocation are distinct. In the standard cluster mapping, an unallocated region can inherit backing data, while an explicit zero cluster masks that data. Reads beyond the end of an existing backing file return zeros. [1]
Verification: Hesela changed one stored payload byte without changing allocation metadata; QEMU 8.2.2 still completed its consistency check successfully. The changed byte was detected by a full export and comparison against the known baseline. This is a controlled example, not a general claim that the checker misses every corruption. [3]
Preservation: identify required backing files as well as the overlay. A top-file hash alone does not identify the entire virtual disk's contents. [2]