---
features:
  - |
    A general framework to accommodate hardware compression accelerators for
    compression of volumes uploaded to the Image service (Glance) as images
    and decompression of compressed images used to create volumes is
    introduced.

    The only accelerator supported in this release is Intel QuickAssist
    Technology (QAT), which produces a compressed file in gzip format.
    Refer to this `Cinder documentation
    <https://docs.openstack.org/cinder/latest/admin/blockstorage-accelerate-image-compression.html>`_
    for more information about using this feature.

    Additionally, the framework provides software-based compression using
    GUNzip tool if a suitable hardware accelerator is not available.
    Because this software fallback could cause performance problems if the
    Cinder services are not deployed on sufficiently powerful nodes, the
    default setting is *not* to enable compression on image upload or
    download.

    The compressed image of a volume will be stored in the
    Image service (Glance) with the ``container_format`` image property of
    ``compressed``.  See the `Image service documentation
    <https://docs.openstack.org/glance/latest>`_ for more information about
    this image container format.
issues:
  - |
    In the Image service (Glance), the ``compressed`` container format
    identifier does not indicate a particular compression technology; it is up
    to the image consumer to determine what compression has been used, and
    there is no requirement that OpenStack services must support arbitrary
    compression technologies.  For the upload and download of compressed
    images, Cinder supports *only* the gzip format.

    While you may expect that Cinder will be able to consume any image in
    ``compressed`` container format *that Cinder has created*, you should not
    expect Cinder to be able to successfully use an image in ``compressed``
    format that it has not created itself.
upgrade:
  - |
    Added string config option ``compression_format`` in [default] section of
    cinder.conf to specify image compression format.  Currently the only legal
    value for this option is ``gzip``.
  - |
    Added boolean config option ``allow_compression_on_image_upload`` in
    [default] section of cinder.conf to enable/disable image compression on
    image upload. The default value of this option is ``false``, which means
    image compression is disabled.