What is a best organization for dbspaces?

Hi Folks, I am trying to find out what is the best plan to organize dbspaces on online 5.x. The manual gives me some guide lines to put rootdb,logical log and phisical log in separate devices to aviod disk congestion and dbspaces with active tables at the center of the device. But how do I locate a center of the device? Is there a way to monitor the disk access times? Thanks in advance. Siva Reddy AT&T