International Business Machines Corporation

Peter L Leung

Brent Cameron Beardsley

Gail Andrea Spear

Susan Kay Candelaria

Vernon John Legvold

James Lincoln Iskiyan

Douglas A Martin

Vern J Legvold

Allen Charles Brailey

Guy E Martin

A system and technique for storing data in a cache memory in record format and in track format. Space is allocated in cache memory for the storage of data in track format. Additional space is allocated for the storage of data in record format. Data is stored in both formats. The most current data is identified and addresses are generated for each record of data. Access to individual records of data is facilitated through a track information block in which pointers are stored for the most current records whether stored in track format or record format. The track information block facilitates a rapid storage and retrieval of data in either format. In a specific implementation, data is stored in either format in cache using a scatter index table. The scatter index table and associated track directory entries are stored in a shared control array. Each track directory entry points to a track slot header in a cache. The track slot header points to an area (segment) in the cache memory in which selected data resides. The track slot header also points to a track information block associated with the selected segment. The track information block identifies the location selected records in the segment in track format or record format.

Track and record mode caching scheme for a storage system employing a

A host processor(s) is loosely-coupled by a plurality of data channels to a peripheral subsystem(s). The host processor(s) has a time of day clock. The peripheral subsystem(s) has a cluster(s) that performs peripheral controller functions. Each cluster has first and second clocks that respectively generate a log entry (logging) reference time and a subsystem time. The first and second clock times result in subsystem time stamps in a log that are not related to the time of day clock. For time correlating the time of day clock with the first and second clocks, a host time stamp is generated from the time of day clock. The host time stamp is sent to the subsystem via one of the data channels for entry into the log with the current time stamps of the first and second clocks as a time-correlating entry. Queue delays in the host processor accessing a data channel for sending the host time stamp and in the subsystem for recording the time-correlating entry are compensated for by updating the host time stamp and by generating an entered time stamp at the time of recording the time-correlating entry. Time stamp correlating operations by a host processor enable recovery from a lost host time stamp.

Using time stamps to correlate data processing event times in connected

Data is accessed by record identification in a peripheral sub-system having cache and back store to transfer the most recently updated version of one or more records stored in the subsystem where one version of a record may be in a back store and a modified version of the record may be in a cache storage, by a method and apparatus including table lookup means for indicating for each record of each track of each device in said back store whether record data stored in cache is modified with respect to a version of the same record stored in back store; and means responsive to the indicating means for transferring the modified or backing store version of a record in accordance with predetermined criteria.

Peripheral subsystem having read/write cache with record access

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Tucson, AZ, United States of America

Peter L Leung