@@ -866,6 +866,37 @@ Supported image file formats:
issue ``lsattr filename`` to check if the NOCOW flag is set or not
(Capital 'C' is NOCOW flag).
+ ``data_file``
+ Filename where all guest data will be stored. If this option is used,
+ the qcow2 file will only contain the image's metadata.
+
+ Note: Data loss will occur if the given filename already exists when
+ using this option with ``qemu-img create`` since ``qemu-img`` will create
+ the data file anew, overwriting the file's original contents. To simply
+ update the reference to point to the given pre-existing file, use
+ ``qemu-img amend``.
+
+ ``data_file_raw``
+ If this option is set to ``on``, QEMU will always keep the external data
+ file consistent as a standalone read-only raw image.
+
+ It does this by forwarding all write accesses to the qcow2 file through to
+ the raw data file, including their offsets. Therefore, data that is visible
+ on the qcow2 node (i.e., to the guest) at some offset is visible at the same
+ offset in the raw data file. This results in a read-only raw image. Writes
+ that bypass the qcow2 metadata may corrupt the qcow2 metadata because the
+ out-of-band writes may result in the metadata falling out of sync with the
+ raw image.
+
+ If this option is ``off``, QEMU will use the data file to store data in an
+ arbitrary manner. The file’s content will not make sense without the
+ accompanying qcow2 metadata. Where data is written will have no relation to
+ its offset as seen by the guest, and some writes (specifically zero writes)
+ may not be forwarded to the data file at all, but will only be handled by
+ modifying qcow2 metadata.
+
+ This option can only be enabled if ``data_file`` is set.
+
``Other``
QEMU also supports various other image file formats for