Managing Serviceguard A.11.20, March 2013

Points to Keep in Mind
The following points apply specifically to the Simple Method (page 150). Read them in conjunction
with the Rules and Guidelines (page 155), which apply to all weights and capacities.
• If you use the reserved CAPACITY_NAME package_limit, then this is the only type of
capacity and weight you can define in this cluster.
• If you use the reserved CAPACITY_NAME package_limit, the default weight for all packages
is 1. You can override this default in the package configuration file, via the weight_name
and weight_value parameters, as in the example above.
(The default weight remains 1 for any package to which you do not explicitly assign a different
weight in the package configuration file.)
• If you use the reserved CAPACITY_NAME package_limit, weight_name, if used, must
also be package_limit.
• You do not have to define a capacity for every node; if you don't, the node is assumed to
have unlimited capacity and will be able to run any number of eligible packages at the same
time.
• If you want to define only a single capacity, but you want the default weight to be zero rather
than 1, do not use the reserved name package_limit. Use another name (for example
resource_quantity) and follow the Comprehensive Method. This is also a good idea if
you think you may want to use more than one capacity in the future.
To learn more about configuring weights and capacities, see the documents listed under For More
Information (page 156).
Comprehensive Method
Use this method if the Simple Method (page 150) does not meet your needs. (Make sure you have
read that section before you proceed.) The comprehensive method works best if packages consume
differing amounts of computing resources, so that simple one-to-one comparisons between packages
are not useful.
IMPORTANT: You cannot combine the two methods. If you use the reserved capacity
package_limit for any node, Serviceguard will not allow you to define any other type of
capacity and weight in this cluster; so you are restricted to the Simple Method in that case.
Defining Capacities
Begin by deciding what capacities you want to define; you can define up to four different capacities
for the cluster.
You may want to choose names that have common-sense meanings, such as “processor”, “memory”,
or “IO”, to identify the capacities, but you do not have to do so. In fact it could be misleading to
identify single resources, such as “processor”, if packages really contend for sets of interacting
resources that are hard to characterize with a single name. In any case, the real-world meanings
of the names you assign to node capacities and package weights are outside the scope of
Serviceguard. Serviceguard simply ensures that for each capacity configured for a node, the
combined weight of packages currently running on that node does not exceed that capacity.
For example, if you define a CAPACITY_NAME and weight_name processor, and a
CAPACITY_NAME and weight_name memory, and a node has a processor capacity of 10
and a memory capacity of 1000, Serviceguard ensures that the combined processor weight
of packages running on the node at any one time does not exceed 10, and that the combined
memory weight does not exceed 1000. But Serviceguard has no knowledge of the real-world
meanings of the names processor and memory; there is no mapping to actual processor and
memory usage and you would get exactly the same results if you used the names apples and
oranges, for example.
152 Planning and Documenting an HA Cluster