In V4R4 a new option is available in the Work with Disk Configuration menu, in the System Service Tools and the Dedicated Service Tools, called Add units to ASPs and balance data. This balancing runs concurrent with normal operations until it is complete. If something could be done to spread the DASD utilization more evenly, overall system performance could be enhanced. It also maintains a utilization level for each DASD unit during this trace period. Furthermore, it identifies units that have high use.
Storage management uses two algorithms when selecting a unit for a new allocation.
The second is for larger allocations where the unit with the greatest percentage of free space is chosen. Once a unit has been identified as being overused, an action can be taken to improve this situation. Cold data, identified as data that is seldom or never referenced, can be moved from an under used unit to the overused unit. Cold data is moved to the over utilized unit to increase its percentage to be sufficiently high enough to keep the system from placing new allocations on this unit. As newer technologies emerge within the DASD subsystems and the system itself, a challenge has been made to the system.