>Is there a preferred db volume size for TSM for optimal performance.

Richard - Not really.  Optimal performance derives from spreading the
          I/O load over multiple db volumes (multiple TSM threads)
and multiple real I/O paths - as well as keeping as much as possible
in real memory.  Many of us use relatively low capacity disks in
quantity to increase the number of disk arms doing writing, to
minimize seeks and rotational delays.

  Richard Sims, BU