System capacity and service group load

The Load and Capacity construct allows the administrator to define a fixed amount of resources a server provides (Capacity), and a fixed amount of resources a specific service group is expected to utilize (Load).

The system attribute Capacity sets a fixed load-handling capacity for servers. Define this attribute based on system requirements.

The service group attribute Load sets a fixed demand for service groups. Define this attribute based on application requirements.

When a service group is brought online, its load is subtracted from the system's capacity to determine available capacity. VCS maintains this info in the attribute AvailableCapacity.

When a failover occurs, VCS determines which system has the highest available capacity and starts the service group on that system. During a failover involving multiple service groups, VCS makes failover decisions serially to facilitate a proper load-based choice.

System capacity is a soft restriction; in some situations, value of the Capacity attribute could be less than zero. During some operations, including cascading failures, the value of the AvailableCapacity attribute could be negative.