Improvements to "Introduction to Object Storage"

Includes:
1. Inclusion of erasure coding info
2. Note about default constraints

backport: mitaka

Change-Id: Ieae09f432b7186391ddad7124e28e0ab3409c94c
Closes-bug: #1596770

doc/config-reference/source/object-storage/about.rst

@@ -2,23 +2,32 @@
 Introduction to Object Storage
 ==============================
 
-Object Storage is a robust, highly scalable and fault tolerant storage platform
-for unstructured data such as objects. Objects are stored bits, accessed
-through a RESTful, HTTP-based interface. You cannot access data at the block or
-file level. Object Storage is commonly used to archive and back up data, with
-use cases in virtual machine image, photo, video and music storage.
+Object Storage (swift) is a robust, highly scalable and fault tolerant storage
+platform for unstructured data such as objects. Objects are stored bits,
+accessed through a RESTful, HTTP-based interface. You cannot access data at
+the block or file level. Object Storage is commonly used to archive and back
+up data, with use cases in virtual machine image, photo, video, and music
+storage.
 
 Object Storage provides a high degree of availability, throughput, and
 performance with its scale out architecture. Each object is replicated across
 multiple servers, residing within the same data center or across data centers,
 which mitigates the risk of network and hardware failure. In the event of
 hardware failure, Object Storage will automatically copy objects to a new
-location to ensure that there are always three copies available. Object Storage
-is an eventually consistent distributed storage platform; it sacrifices
-consistency for maximum availability and partition tolerance. Object Storage
-enables you to create a reliable platform by using commodity hardware and
-inexpensive storage.
+location to ensure that your chosen number of copies are always available.
 
-For more information, review the key concepts in the developer documentation at
-`docs.openstack.org/developer/swift/
+Object Storage also employs erasure coding. Erasure coding is a set of
+algorithms that allows the reconstruction of missing data from a set of
+original data. In theory, erasure coding uses less storage capacity with
+similar durability characteristics as replicas. From an application
+perspective, erasure coding support is transparent. Object Storage
+implements erasure coding as a Storage Policy.
+
+Object Storage is an eventually consistent distributed storage platform;
+it sacrifices consistency for maximum availability and partition tolerance.
+Object Storage enables you to create a reliable platform by using commodity
+hardware and inexpensive storage.
+
+For more information, review the key concepts in the developer documentation
+at `docs.openstack.org/developer/swift/
 <http://docs.openstack.org/developer/swift/>`__.

doc/config-reference/source/object-storage/general-service-conf.rst

@@ -5,8 +5,8 @@ Object Storage general service configuration
 Most Object Storage services fall into two categories, Object Storage's WSGI
 servers and background daemons.
 
-Object Storage uses paste.deploy to manage server configurations. Read more at
-http://pythonpaste.org/deploy/.
+Object Storage uses ``paste.deploy`` to manage server configurations.
+Read more at `<http://pythonpaste.org/deploy/>`_.
 
 Default configuration options are set in the ``[DEFAULT]`` section, and any
 options specified there can be overridden in any of the other sections when the
@@ -38,6 +38,12 @@ the ``object-server``, ``object-updater``, ``object-replicator``, and
 
     [object-auditor]
 
+.. note::
+
+   Default constraints can be overridden in ``swift.conf``. For example,
+   you can change the maximum object size and other variables.
+
+
 Object Storage services expect a configuration path as the first argument:
 
 .. code-block:: console