Patent ID: 6021463
Filing Date: 2000-02-01
Classification: G06F,G11B,Y10S

Abstract:
In a subsystem for accessing addressable ECC-coded sectors of magnetic disk tracks of a DASD subject to sector level redundancy group organization, a method for managing write updates to said addressable sectors and for maintaining fault tolerance of counterpart redundancy groups, comprising the steps of:(a) maintaining a current set of all redundant sectors and a concordance of sectors and redundancy groups in a subsystem memory external to the DASD;(b) responsive to a write update to a given addressed sector, ascertaining the redundancy group to which the given sector is a member, and copying into a subsystem buffer (1) the counterpart redundant sector from the subsystem memory, (2) the given addressed sector into the buffer if present in the subsystem, or if not, staging the given addressed sector from the DASD, and (3) the updated sector; and(c) forming an updated redundant sector by logically combining the redundant sector from the subsystem memory, the given sector, and the updated sector; and(d) copying the updated redundant sector into the subsystem memory and asynchronously writing out the modified sector in place on the DASD disk tracks such that only a read access of the DASD sector to be updated need be made because of the availability of the updated sector and the given redundant sector information at the subsystem.