To make efficient use of cache structure storage, you need to cast-out the changed data in a timely way by using REQUEST=CASTOUT_DATA and ensure that you release the lock for the data items you have cast out by using REQUEST=UNLOCK_CASTOUT. Once the changed data item is cast out and the lock for the data item is released, the resources for the data item are eligible for reclaim. For information, see Reasons for Casting out Data.