Different types of resources require different types of control, requiring implementation of different entry points. Resources can be classified as on-off, on-only, or persistent.
Most resources are on-off, meaning agents start and stop them as required. For example, VCS assigns an IP address to a specified NIC when bringing a resource online and removes the assigned IP address when taking the resource offline. Another example is the DiskGroup resource. The engine imports a disk group when needed and deports it when it is no longer needed. For agents of on-off resources, all entry points can be implemented.
An on-only resource is brought online, but it is not taken offline when the associated service group is taken offline. For example, in the case of the FileOnOnly resource, the engine creates the specified file when required, but does not delete the file if the associated service group is taken offline. For agents of on-only resources, the offline entry point is not needed or invoked.
A persistent resource cannot be brought online or taken offline, yet the resource must be present in the configuration to allow the resource to be monitored. For example, a NIC resource cannot be started or stopped, but it is required to be operational in order for the associated IP address to function properly. The agent monitors persistent resources to ensure their status and operation. An agent for a persistent resource does not require or invoke the online or offline entry points. It uses only the monitor entry points.