Add glossary for some common terms

Change-Id: I3868b20fdd2d6cdff73e153d5022ad7c1b4f3c5d

doc/source/glossary.rst

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+.. _Glossary:
+
+############
+Glossary
+############
+
+.. _B:
+
+****
+B
+****
+
+.. _Backup:
+
+**Backup**
+
+  A single backup containing refence to all objects needed to reassemble a disk
+  image. A backup would reference all `Segment`_ and a `Manifest`_. A backup
+  is part of a `Backupset`_.
+
+.. _Backupset:
+
+**Backupset**
+
+  A backupset is a uuid used to provide a unique identifier to a collection of
+  backups allowing for thier location in storage to be non-conflicting with
+  other backupsets. A backupset references a single disk in an instance. When a
+  `Restore`_ is preformed and a new `Backup`_ is started and new backupset uuid
+  would be generated.
+
+.. _M:
+
+****
+M
+****
+
+.. _Manifest:
+
+**Manifest**
+
+  A manifest is a file that tracks metadata and information about a single
+  `Backup`_. It has enough information to locate each `Segment`_ that is
+  required to bit-for-bit reassemble the block device the `Backup`_ was taken
+  from.
+
+.. _R:
+
+****
+R
+****
+
+.. _Restore:
+
+**Restore**
+
+  A restore refers to reassembling a `Backup`_ from it's backing storage into
+  an image that can then be booted or otherwise attached to an instance. It
+  reads the `Manifest`_ of the `Backup`_ that you want to restore and pulls all
+  of the appropriate objects and then unencrypts and uncompresses them before
+  reassembling the final image and uploading it to Glance.
+
+.. _S:
+
+****
+S
+****
+
+.. _Segment:
+
+**Segment**
+
+  A segment is a section of the block device. It is typially 4MiB in size. A
+  `Manifest`_ contains a list of segments that, when combined, would produce a
+  bit-for-bit copy of the original block device the `Backup`_ was taken from.