What's the difference between Agents and Resources?

Agents are VCS processes that control and monitor the Resources. Resources are all those objects in your Service Group, and they all require Agents.

For example, all your filesystems are resources, and they all use the Mount Agent. Your virtual IP address is a resource, and it uses the IP or IPMultiNIC Agent. The Veritas Volume Manager Disk Group is a resource, and it uses the DiskGroup Agent. Some Agents, such as the Oracle Enterprise Agent, have to be purchased separately.