Update AFS fileserver settings

Jeffrey Altman has pointed out that our settings are not optimal for
our use cases.  Turning up threads and callbacks is a start.  We
should evaluate the other settings too.

Add notes on how to apply settings manually

Change-Id: I1405b21f97c1ac2d3bd99ffbba18e5fd0ff959b1

doc/source/afs.rst

@@ -190,12 +190,49 @@ Create an LVM volume named ``vicepa`` from cinder volumes.  See
 
 Finally, create the fileserver with::
 
-  bos create NEWSERVER dafs dafs \
+  bos create -server NEWSERVER -instance dafs -type dafs \
-    -cmd "/usr/lib/openafs/dafileserver -p 23 -busyat 600 -rxpck 400 -s 1200 -l  1200 -cb 65535 -b 240 -vc 1200" \
+    -cmd "/usr/lib/openafs/dafileserver -L -p 242 -busyat 600 -rxpck 700 \
+      -s 1200 -l 1200 -cb 1500000 -b 240 -vc 1200 \
+      -udpsize 131071 -sendsize 131071" \
     -cmd /usr/lib/openafs/davolserver \
     -cmd /usr/lib/openafs/salvageserver \
     -cmd /usr/lib/openafs/dasalvager
 
+It is worth evaluating these settings periodically
+
+* ``-L`` selects the large size, which ups a number of defaults
+* ``-p`` defines the worker threads for processing incoming calls.
+  Since they block until there is work to do, we should leave this at
+  around the maximum (which may increase across versions; see
+  documentation)
+* ``-udpsize`` and ``-sendsize`` should be increased above their default
+* ``-cb`` defines the callbacks.  For our use case, with a single
+  mirror writer, this should be around the number of files the client
+  is configured to cache (``-dcache``) multiplied by the number of
+  clients.
+
+Updating Settings
+~~~~~~~~~~~~~~~~~
+
+If you wish to update the settings for an existing server, you can
+stop and remove the existing ``bnode`` (the collection of processes
+the overseeer is monitoring, created via ``bos create`` above) and
+recreate it.
+
+For example ::
+
+  bos stop -server afs01.dfw.openstack.org \
+           -instance dafs \
+           -wait
+
+Then remove the server with ::
+
+  bos delete -server afs01.dfw.openstack.org \
+             -instance dafs
+
+Finally run the ``bos create`` command above with any modified
+parameters to restart the server.
+
 Mirrors
 ~~~~~~~