International Business Machines Corporation

Michael F Mitoma

Steven Robert Hetzler

Jaishankar Moothedath Menon

John Stewart Best

Roger F Hoyt

A method for operating a synchronized array of fixed block (FBA) formatted Direct Access Storage Devices (DASDs) to store and update variable-length (CKD) formatted records. This method is suitable for use with DASDs that obtain high recording density by using read and write head technology requiring 'micro-jogging' to adjust for differing read and write head alignment or banded disk architecture having a higher block count in the outer tracks than in the inner tracks. Magneto-resistive heads may require micro-jogging to realign the write head for recording after reading the physical track location. The invention employs a DASD staggered array architecture having logical tracks consisting of diagonal-major sequences of consecutive blocks arranged in a predetermined wrap-around manner such as a topological cylinder or torus. The minimum necessary number of DASDs (N) in the staggered array is limited by the fixed block size (B), the interblock gap size (G), the average DASD data transfer rate (D), and the micro-jog delay time (T). A (N+1).sup.th DASD may be added to record the parity of each diagonal-major sequence for improved fault-tolerance.

Efficient variable-block data storage system employing a staggered

One or more data-storing disk devices support logical tracks extending between radial recording zones of tracks in the device(s). Each data-storing disk in the device(s) is formatted into a plurality of radial recording zones of physical tracks, each radial recording zone having a like number of physical tracks, each physical track may be one circumvolution of a single spiral track. The physical tracks in the respective recording zones store a different number of data bytes. Each logical track including a plurality of said physical tracks; at least one of the physical tracks in each of the logical tracks is in a different one of the radial recording zones in different ones of the devices or in a single device. Described are an extended logical track and extended logical cylinder accessing methods and apparatus. Not all of the physical tracks of any of the devices or recording zones need be a member of any logical track.

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San Jose, CA, United States of America

Michael F Mitoma