[config-ref] Migrate section_block-storage-overview.xml to rst

Change-Id: I6f763f715106776960536b769a4feb3a5c06dbe0
Implements: blueprint config-ref.rst

doc/config-ref-rst/source/block-storage/block-storage-overview.rst

@@ -1,3 +1,89 @@
 =========================================
 Introduction to the Block Storage service
 =========================================
+
+The Block Storage service provides persistent block storage
+resources that Compute instances can consume. This includes
+secondary attached storage similar to the Amazon Elastic Block Storage
+(EBS) offering. In addition, you can write images to a Block Storage
+device for Compute to use as a bootable persistent instance.
+
+The Block Storage service differs slightly from the Amazon EBS offering.
+The Block Storage service does not provide a shared storage solution
+like NFS. With the Block Storage service, you can attach a device to
+only one instance.
+
+The Block Storage service provides:
+
+-  ``cinder-api`` - a WSGI app that authenticates and routes requests
+   throughout the Block Storage service. It supports the OpenStack APIs
+   only, although there is a translation that can be done through
+   Compute's EC2 interface, which calls in to the Block Storage client.
+
+-  ``cinder-scheduler`` - schedules and routes requests to the appropriate
+   volume service. Depending upon your configuration, this may be simple
+   round-robin scheduling to the running volume services, or it can be
+   more sophisticated through the use of the Filter Scheduler. The
+   Filter Scheduler is the default and enables filters on things like
+   Capacity, Availability Zone, Volume Types, and Capabilities as well
+   as custom filters.
+
+-  ``cinder-volume`` - manages Block Storage devices, specifically the
+   back-end devices themselves.
+
+-  ``cinder-backup`` - provides a means to back up a Block Storage volume to
+   OpenStack Object Storage (swift).
+
+The Block Storage service contains the following components:
+
+-  **Back-end Storage Devices** - the Block Storage service requires some
+   form of back-end storage that the service is built on. The default
+   implementation is to use LVM on a local volume group named
+   "cinder-volumes." In addition to the base driver implementation, the
+   Block Storage service also provides the means to add support for
+   other storage devices to be utilized such as external Raid Arrays or
+   other storage appliances. These back-end storage devices may have
+   custom block sizes when using KVM or QEMU as the hypervisor.
+
+-  **Users and Tenants (Projects)** - the Block Storage service can be
+   used by many different cloud computing consumers or customers
+   (tenants on a shared system), using role-based access assignments.
+   Roles control the actions that a user is allowed to perform. In the
+   default configuration, most actions do not require a particular role,
+   but this can be configured by the system administrator in the
+   appropriate ``policy.json`` file that maintains the rules. A user's
+   access to particular volumes is limited by tenant, but the user name
+   and password are assigned per user. Key pairs granting access to a
+   volume are enabled per user, but quotas to control resource
+   consumption across available hardware resources are per tenant.
+
+   For tenants, quota controls are available to limit:
+
+   -  The number of volumes that can be created.
+
+   -  The number of snapshots that can be created.
+
+   -  The total number of GBs allowed per tenant (shared between
+      snapshots and volumes).
+
+   You can revise the default quota values with the Block Storage CLI,
+   so the limits placed by quotas are editable by admin users.
+
+-  **Volumes, Snapshots, and Backups** - the basic resources offered by
+   the Block Storage service are volumes and snapshots which are derived
+   from volumes and volume backups:
+
+   -  **Volumes** - allocated block storage resources that can be
+      attached to instances as secondary storage or they can be used as
+      the root store to boot instances. Volumes are persistent R/W block
+      storage devices most commonly attached to the compute node through
+      iSCSI.
+
+   -  **Snapshots** - a read-only point in time copy of a volume. The
+      snapshot can be created from a volume that is currently in use
+      (through the use of ``--force True``) or in an available state.
+      The snapshot can then be used to create a new volume through
+      create from snapshot.
+
+   -  **Backups** - an archived copy of a volume currently stored in
+      Object Storage (swift).