When you write changed data to the cache, you must assign the data to a cast-out class. Cast-out class assignments help to implement the cast-out process whereby changed data from the cache structure is written to permanent storage. Until the data item is successfully cast out from the cache structure, the system cannot reclaim resources for the changed data item. The system considers a data item to be changed, and thus ineligible for reclaim, if either of the following conditions is true:

• The data item's directory entry is marked changed.
• The data item's cast-out lock is held. (When the cast-out lock is released, the data item is considered unchanged.)