Add doc page for accelerate image compression

The related code review:
https://review.opendev.org/#/c/668825/

Change-Id: I5485f7f935c43a920f9c065ab9cf5ca300fa002a
Signed-off-by: Liang Fang <liang.a.fang@intel.com>

doc/source/admin/blockstorage-accelerate-image-compression.rst

@@ -0,0 +1,59 @@
+.. _accelerate_image_compression:
+
+
+============================
+Accelerate image compression
+============================
+
+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 in
+Train release.
+
+The only accelerator supported in this release is Intel QuickAssist Technology
+(QAT), which produces a compressed file in gzip format.  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.
+
+Configure image compression
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To enable the image compression feature, set the following configuration option
+in the ``cinder.conf`` file:
+
+.. code-block:: ini
+
+   allow_compression_on_image_upload = True
+
+By default it will be set to False, which means image compression is disabled.
+
+.. code-block:: ini
+
+   compression_format = gzip
+
+This is to specify image compression format. The only supported format is
+``gzip`` in Train release.
+
+System requirement
+~~~~~~~~~~~~~~~~~~
+
+In order to use this feature, there should be a hardware accelerator existing
+in system, otherwise no benefit will get from this feature. Regarding the two
+accelerators that supported, system should be configured as below:
+
+- ``Intel QuickAssist Technology (QAT)`` - This is the hardware accelerator
+  from Intel. The driver of QAT should be installed, refer to
+  https://01.org/intel-quickassist-technology. Also the compression library
+  QATzip should be installed, refer to https://github.com/intel/QATzip.
+
+- ``GUNzip`` - The related package of ``GUNzip`` should be installed and the
+  command ``gzip`` should be available. This is used as fallback when hardware
+  accelerator is not available.

doc/source/admin/index.rst

@@ -24,6 +24,7 @@ Amazon EC2 Elastic Block Storage (EBS) offering.
 .. toctree::
    :maxdepth: 1
 
+   blockstorage-accelerate-image-compression.rst
    blockstorage-api-throughput.rst
    blockstorage-manage-volumes.rst
    blockstorage-troubleshoot.rst