About defining failover policies

The service group attribute FailOverPolicy governs how VCS calculates the target system for failover.

Table: Possible values of the FailOverPolicy attribute and their description shows the possible values for the attribute FailoverPolicy.

Table: Possible values of the FailOverPolicy attribute and their description

FailOverPolicy attribute value

Description

Priority

VCS selects the system with the lowest priority as the failover target. The Priority failover policy is ideal for simple two-node clusters or small clusters with few service groups.

Priority is set in the SystemList attribute implicitly by ordering, such as SystemList = {SystemA, SystemB} or explicitly, such as SystemList = {SystemA=0, SystemB=1}. Priority is the default behavior.

RoundRobin

VCS selects the system running the fewest service groups as the failover target. This policy is ideal for large clusters running many service groups with similar server load characteristics (for example, similar databases or applications)

Load

The Load failover policy comprises the following components:

System capacity and service group load, represented by the attributes Capacity and Load respectively.

See System capacity and service group load.

System limits and service group prerequisites, represented by the attributes Limits and Prerequisites, respectively.

You cannot set the service group attribute FailOverPolicy to Load if the cluster attribute Statistics is enabled.

See System limits and service group prerequisites.

BiggestAvailable

VCS selects a system based on the forecasted available capacity for all systems in the SystemList. The system with the highest forecasted available capacity is selected.

This policy can be set only if the cluster attribute Statistics is set to Enabled. The service group attribute Load is defined in terms of CPU, Memory, and Swap in absolute units. The unit can be of the following values:

  • CPU, MHz, or GHz for CPU

  • GB or MB for Memory

  • GB or MB for Swap

See Cluster attributes.