Add LVM2/iSCSI documentation

This patch adds to cinder-guide.rst LVM2/iSCSI related
information.

TrivialFix

Change-Id: I2c7b3090bbf314dd1281ca3d02148490936d5b86

doc/cinder-guide.rst

@@ -75,3 +75,60 @@ Check the console log added the disk:
 A /dev/vdb should appear in the console log, at least when booting cirros.
 If the disk stays in the available state, something went wrong during the
 iSCSI mounting of the volume to the guest VM.
+
+Cinder LVM2 backend with iSCSI
+------------------------------
+As of Newton-1 milestone, Kolla supports LVM2 as cinder backend. It is
+accomplished by introducing two new containers tgtd and iscsid.
+tgtd container serves as a bridge between cinder-volume process and a server
+hosting Logical Volume Groups (LVG). iscsid container serves as a bridge
+between nova-compute process and the server hosting LVG.
+
+There are two methods to apply new configuration to cinder:
+ 1 - New deployments: create cinder.conf and place it at /etc/kolla/config
+     folder, then add below configuration lines and run kolla deloyment.
+ 2 - Existing cinder deployments: modify cinder.conf located at
+     /etc/kolla/config by adding below configuration lines and run kolla
+     reconfigure.
+
+::
+
+    [DEFAULT]
+    enabled_backends = {local_lvm_name}
+    volume_name_template=volume-%s
+
+    [{local_lvm_name}]
+    lvm_type = default
+    volume_group = {lvg_name}
+    volume_driver = cinder.volume.drivers.lvm.LVMVolumeDriver
+    volume_backend_name = {local_lvm_name}
+    iscsi_helper=tgtadm
+    iscsi_ip_address={management_ip_address_of_server_hosting_LVG}
+    iscsi_protocol=iscsi
+::
+
+Where:
+
+- local_lvm_name is a name chosen by a user for a spefic LVM2 backend, multiple
+LVM2 backend can be confiugred and each should have a unique name.
+
+- lvg_name is a name Logical Volume Group created for cinder to store volumes.
+
+- management_ip_address_of_server_hosting_LVG is IP address of an interface
+where cinder process is bound to. (Do not use VIP address here, LVG does not
+move from server to server as VIP address does in case of a server failure).
+
+NOTE: For Ubuntu and LVM2/iSCSI
+
+iscsd process uses configfs which is normally mounted at /sys/kernel/config to
+store discovered targets information, on centos/rhel type of systems this special
+file system gets mounted automatically, which is not the case on debian/ubuntu.
+Since iscsid container runs on every nova compute node, the following steps must
+be completed on every Ubuntu server targeted for nova compute role.
+
+ 1 - Add configfs module to /etc/modules
+ 2 - Rebuild initramfs using: "update-initramfs -u" command
+ 3 - Make sure configfs gets mounted during a server boot up process. There are
+     multiple ways to accomplish it, one example is adding this command to
+     "mount -t configfs configfs /sys/kernel/config" to /etc/rc.local
+