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qemu-img: Update documentation for compressed images

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Document the 'compression_type' option for qcow2, and mention that
streamOptimized vmdk supports compression, too.

Reported-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230901102430.23856-1-kwolf@redhat.com>
Reviewed-by: Richard W.M. Jones <rjones@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2023-09-01 12:24:30 +02:00
parent 816248675a
commit a675ca4c62
1 changed files with 17 additions and 2 deletions
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19
docs/tools/qemu-img.rst
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@ -106,7 +106,11 @@ by the used format or see the format descriptions below for details.
.. option:: -c .. option:: -c
Indicates that target image must be compressed (qcow format only). Indicates that target image must be compressed (qcow/qcow2 and vmdk with
streamOptimized subformat only).
For qcow2, the compression algorithm can be specified with the ``-o
compression_type=...`` option (see below).
.. option:: -h .. option:: -h
@ -776,7 +780,7 @@ Supported image file formats:
QEMU image format, the most versatile format. Use it to have smaller QEMU image format, the most versatile format. Use it to have smaller
images (useful if your filesystem does not supports holes, for example images (useful if your filesystem does not supports holes, for example
on Windows), optional AES encryption, zlib based compression and on Windows), optional AES encryption, zlib or zstd based compression and
support of multiple VM snapshots. support of multiple VM snapshots.
Supported options: Supported options:
@ -794,6 +798,17 @@ Supported image file formats:
``backing_fmt`` ``backing_fmt``
Image format of the base image Image format of the base image
``compression_type``
This option configures which compression algorithm will be used for
compressed clusters on the image. Note that setting this option doesn't yet
cause the image to actually receive compressed writes. It is most commonly
used with the ``-c`` option of ``qemu-img convert``, but can also be used
with the ``compress`` filter driver or backup block jobs with compression
enabled.
Valid values are ``zlib`` and ``zstd``. For images that use
``compat=0.10``, only ``zlib`` compression is available.
``encryption`` ``encryption``
If this option is set to ``on``, the image is encrypted with If this option is set to ``on``, the image is encrypted with
128-bit AES-CBC. 128-bit AES-CBC.