tweaks per jesse comments

stack.sh

@@ -546,9 +546,9 @@ if [[ "$ENABLED_SERVICES" =~ "n-vol" ]]; then
     #
     # By default, the backing file is 2G in size, and is stored in /opt/stack.
     #
-    VOLUME_BACKING_FILE=${VOLUME_BACKING_FILE:-/opt/stack/nova-volumes-backing-file}
-    VOLUME_BACKING_FILE_SIZE=${VOLUME_BACKING_FILE_SIZE:-2052M}
     if ! sudo vgdisplay | grep -q nova-volumes; then
+        VOLUME_BACKING_FILE=${VOLUME_BACKING_FILE:-/opt/stack/nova-volumes-backing-file}
+        VOLUME_BACKING_FILE_SIZE=${VOLUME_BACKING_FILE_SIZE:-2052M}
         truncate -s $VOLUME_BACKING_FILE_SIZE $VOLUME_BACKING_FILE
         DEV=`sudo losetup -f --show $VOLUME_BACKING_FILE`
         sudo vgcreate nova-volumes $DEV

tools/build_lxc.sh

@@ -38,7 +38,7 @@ DEST=${DEST:-/opt/stack}
 WAIT_TILL_LAUNCH=${WAIT_TILL_LAUNCH:-1}
 
 # Param string to pass to stack.sh.  Like "EC2_DMZ_HOST=192.168.1.1 MYSQL_USER=nova"
-# By default, n-vol is disabled for lxc
+# By default, n-vol is disabled for lxc, as iscsitarget doesn't work properly in lxc
 STACKSH_PARAMS=${STACKSH_PARAMS:-"ENABLED_SERVICES=g-api,g-reg,key,n-api,n-cpu,n-net,n-sch,n-vnc,dash,mysql,rabbit"}
 
 # Option to use the version of devstack on which we are currently working