Directory rebuild method and apparatus for maintaining and rebuilding directory information for compressed data on direct access storage device (DASD)

摘要

A method and apparatus for maintaining and rebuilding directory information for compressed data on a direct access storage device are provided. A directory of DASD compressed data is stored in the storage controller and directory information is periodically written to the DASD for compressed data written to the DASD. A drive write count (DWC) of each write operation to the DASD is maintained. A number of sectors in a compressed data page is identified for the drive write count. A sector sequence number is identified for each of the number of sectors in the compressed data page. A span for the compressed data page is identified for the drive write count. A page offset is identified for the identified number of sectors in the compressed data page. A deallocation status of a first page of an extent is identified. The extent is a block of sequential compressed data pages. Compressed data is written to the DASD with a compression sector header including the drive write, the identified number of sectors, the identified write length indicator, the identified page offset, the identified span, and the identified deallocation status. Directory recovery is performed by reading compressed data from the DASD and utilizing the compression sector header to enable reclamation of valid sequences of DASD sectors into compressed pages.