Abstract: An apparatus and method for storing track layout information for performing update write operations is provided. In particular, the present invention provides an apparatus and method for storing track layout information based on cylinders which is then used to verify a quick write operation. A quick write operation is an update write operation in which track data need not be read from the physical storage device before performing an update of one or more records in the track. With the present invention, as tracks are written to or read from a storage device, such as a DASD or Non-Volatile Store (NVS), a cylinder table is populated with information identifying the tracks that meet criteria set for identifying tracks that are candidates for future quick write operations. The track layout information is stored on a cylinder basis.

Abstract: Each time a track is referenced, a value representing the last referenced age is entered for a track entry in a last referenced age table (LRAT). The last referenced age table is indexed by track. A second table, an age frequency table (AFT), counts all segments in use in each reference age. The AFT is indexed by the reference age of the tracks. When a track is referenced, the number of segments used for the track is added to a segment count associated with the last referenced age of the track. The segment count tallies the total number of segments in use for the reference age for all tracks referenced to that age. The number of segments used for the previous last referenced age of the track is subtracted from the segment count associated with the previous last referenced age in the AFT. When free_space is needed, tracks are discarded from the LRAT by reference age, the oldest first.