Update Install Guide for Glance for Newton

Updates:
- Removed references to the S3 backend, whose driver was removed with
  change I032b0fc16400cbd2112687d38e010128be699221
- Clarified use of filesystem store, based on an actual question
  asked in #openstack-glance
- Expanded the list of backends mentioned where appropriate

Change-Id: Ic0220a714beadd54cdf0c86ce65ab9223a88a3de

doc/common/get-started-image-service.rst

@@ -33,8 +33,10 @@ Database
 
 Storage repository for image files
   Various repository types are supported including normal file
-  systems, Object Storage, RADOS block devices, HTTP, and Amazon S3.
-  Note that some repositories will only support read-only usage.
+  systems (or any filesystem mounted on the glance-api controller
+  node), Object Storage, RADOS block devices, VMware datastore,
+  and HTTP. Note that some repositories will only support read-only
+  usage.
 
 Metadata definition service
   A common API for vendors, admins, services, and users to meaningfully

doc/common/glossary.rst

@@ -387,7 +387,8 @@ B
       for a service, such as lists of Object Storage objects, current state
       of guest VMs, lists of user names, and so on. Also, the method that the
       Image service uses to get and store VM images. Options include Object
-      Storage, local file system, S3, and HTTP.
+      Storage, locally mounted file system, RADOS block devices, VMware
+      datastore, and HTTP.
 
    backup restore and disaster recovery as a service
 
@@ -1874,7 +1875,8 @@ I
    image store
 
       The back-end store used by Image service to store VM images,
-      options include Object Storage, local file system, S3, or HTTP.
+      options include Object Storage, locally mounted file system,
+      RADOS block devices, VMware datastore, or HTTP.
 
    image UUID
 
@@ -3251,11 +3253,6 @@ S
 
 .. glossary::
 
-   S3
-
-      Object storage service by Amazon; similar in function to Object
-      Storage, it can act as a back-end store for Image service VM images.
-
    sahara
 
       OpenStack project that provides a scalable data-processing stack

doc/install-guide/source/glance.rst

@@ -24,7 +24,9 @@ systems to object-storage systems like OpenStack Object Storage.
    default, this directory is ``/var/lib/glance/images/``.
 
    Before you proceed, ensure that the controller node has at least
-   several gigabytes of space available in this directory.
+   several gigabytes of space available in this directory.  Keep in
+   mind that since the ``file`` back end is often local to a controller
+   node, it is not typically suitable for a multi-node glance deployment.
 
    For information on requirements for other back ends, see
    `Configuration Reference <http://docs.openstack.org/mitaka/config-reference/image-service.html>`__.