When to use Subsets in the DSM Manager

[jeffturl_1]

On our W2K3 servers we have MPIO Fully featured and the DSM for the EVA6400 installed.  Also on the servers is the MPIO DSM Manager.  The MPIO DSM manager is currently configured on the 2003 Servers so that subsets are enabled.  in the DSM manager for each lun there are 16 paths (2 port HBA in the server connecting to a two switch fabric). 

Each disk has ALB enabled, and of the 8 paths are in the subset and show as state Active and are configured to go to teh preferred controller .  The other 8 paths to thd non preferred controller show as available. 

In CV the controller is set to either A or B and also set to failover/failback, which tallys with the subset configured on the windows servers. so all 8 paths that show as active are going to the controller which is the preferred owner.

So it all sounds good to me, however what are subsets, should they be being used in this way? is this what they are designed to do?  it seems very ganular control over which paths are used for active I/O is this correct?

Regards
Jeff