.. Licensed to the Apache Software Foundation (ASF) under one
   or more contributor license agreements.  See the NOTICE file
   distributed with this work for additional information#
   regarding copyright ownership.  The ASF licenses this file
   to you under the Apache License, Version 2.0 (the
   "License"); you may not use this file except in compliance
   with the License.  You may obtain a copy of the License at
   http://www.apache.org/licenses/LICENSE-2.0
   Unless required by applicable law or agreed to in writing,
   software distributed under the License is distributed on an
   "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   KIND, either express or implied.  See the License for the
   specific language governing permissions and limitations
   under the License.
   

Tuning
======

This section provides tips on how to improve the performance of your
cloud.


Performance Monitoring
----------------------

Host and guest performance monitoring is available to end users and
administrators. This allows the user to monitor their utilization of
resources and determine when it is appropriate to choose a more powerful
service offering or larger disk.


Increase Management Server Maximum Memory
-----------------------------------------

If the Management Server is subject to high demand, the default maximum
JVM memory allocation can be insufficient. To increase the memory:

#. Edit the Tomcat configuration file:

   .. code:: bash

      /etc/cloudstack/management/tomcat6.conf

#. Change the command-line parameter -XmxNNNm to a higher value of N.

   For example, if the current value is -Xmx128m, change it to -Xmx1024m
   or higher.

#. To put the new setting into effect, restart the Management Server.

   .. code:: bash

      # service cloudstack-management restart

For more information about memory issues, see "FAQ: Memory" at `Tomcat
Wiki. <http://wiki.apache.org/tomcat/FAQ/Memory>`_


Set Database Buffer Pool Size
-----------------------------

It is important to provide enough memory space for the MySQL database to
cache data and indexes:

#. Edit the MySQL configuration file:

   .. code:: bash

      /etc/my.cnf

#. Insert the following line in the [mysqld] section, below the datadir
   line. Use a value that is appropriate for your situation. We
   recommend setting the buffer pool at 40% of RAM if MySQL is on the
   same server as the management server or 70% of RAM if MySQL has a
   dedicated server. The following example assumes a dedicated server
   with 1024M of RAM.

   .. code:: bash

      innodb_buffer_pool_size=700M

#. Restart the MySQL service.

   .. code:: bash

      # service mysqld restart

For more information about the buffer pool, see "The InnoDB Buffer Pool"
at `MySQL Reference
Manual <http://dev.mysql.com/doc/refman/5.5/en/innodb-buffer-pool.html>`_.


Set and Monitor Total VM Limits per Host
----------------------------------------

The CloudStack administrator should monitor the total number of VM
instances in each cluster, and disable allocation to the cluster if the
total is approaching the maximum that the hypervisor can handle. Be sure
to leave a safety margin to allow for the possibility of one or more
hosts failing, which would increase the VM load on the other hosts as
the VMs are automatically redeployed. Consult the documentation for your
chosen hypervisor to find the maximum permitted number of VMs per host,
then use CloudStack global configuration settings to set this as the
default limit. Monitor the VM activity in each cluster at all times.
Keep the total number of VMs below a safe level that allows for the
occasional host failure. For example, if there are N hosts in the
cluster, and you want to allow for one host in the cluster to be down at
any given time, the total number of VM instances you can permit in the
cluster is at most (N-1) \* (per-host-limit). Once a cluster reaches
this number of VMs, use the CloudStack UI to disable allocation of more
VMs to the cluster.


Configure XenServer dom0 Memory
-------------------------------

Configure the XenServer dom0 settings to allocate more memory to dom0.
This can enable XenServer to handle larger numbers of virtual machines.
We recommend 2940 MB of RAM for XenServer dom0. For instructions on how
to do this, see `Citrix Knowledgebase
Article <http://support.citrix.com/article/CTX126531>`_.The article
refers to XenServer 5.6, but the same information applies to XenServer 6