International Business Machines Corporation

Barrie N Harding

Steven D Gerdt

Lloyd R Shipman, Jr

Dennis R Escola

Bruce McNutt

Gary Eugene Morain

Paul W Hunter

Dennis Carl Mairet

Ruth Enid Azevedo

Michael Allen Griese

The present invention provides a system for configuration and running a DASD storage subsystem where the small computer system interface (SCSI) Target behavior needs to be different depending on type and characteristics of the attaching SCSI hosts. The configuration process defines the behavior by SCSI bus port through the use of bus behavior tables. Accordingly, several ports are able to operate correctly based on the hosts that attach to separate ports. In a first aspect, a direct access storage device (DASD) storage subsystem is described. The DASD storage subsystem comprises a plurality of ports, each of the plurality of ports including a table. Each of the tables defines the behavior of the particular port as a SCSI target. The DASD storage subsystem includes a mechanism for configuring the plurality of ports utilizing the tables within the ports. In a second aspect, a SCSI system is described. The SCSI system comprises a plurality of SCSI hosts and a DASD storage subsystem. The DASD storage subsystem comprises a plurality of ports. Each of the plurality of ports is coupled to one or more of the plurality of SCSI hosts. Each of the plurality of ports includes a table. Each of the tables defines the behavior of the particular port as a SCSI target. The DASD storage subsystem also includes a mechanism for configuring the plurality of ports utilizing the tables within the ports.

Method and system for allowing a plurality of SCSI hosts to interact

A cache management system for dynamically switching between record caching and track caching. Statistics are collected within the cache management system to determine the type and amount of locality associated with a specific data set currently within the cache. Using these statistics, metrics of the actual hit ratio, whole-track hit ratio, and other-record-hit ratio are generated. The metrics are periodically reviewed for a given band, and the band is placed into one of three cache modes accordingly. The mode assignment determines what type of staging will be performed for data within the band in the event of a miss. The possible modes are: track mode for track-based staging, record mode for staging of a single record only, or uncached mode if no data is to be staged. If a band has been assigned to either record or track mode, the assignment is re-evaluated after for a predetermined number of I/O's (128). If the band has been assigned to uncached mode, then after another predetermined number of I/O's (4096), the band is reassigned to record mode in order to force an update of the band statistics.

Aggressive adaption algorithm for selective record caching

A data storage and retrieval system is described having one or more key-lock storage areas which can be modified under the control of commands received from an attached computer. Each key-lock is stored in nonvolatile data storage. A key-lock contains a key field and a lock field. The contents of the key-lock are read and modified based on commands received from the computer. The command to write a new key-lock value specifies a first key and a proffered key-lock. The subsystem reads the current key-lock from nonvolatile storage, then compares the first and current keys. When the first and current keys are equal, the proffered key-lock is stored in the key-lock storage area of nonvolatile data storage, thereby replacing the original key-lock. When the keys are not equal, the key-lock is left unmodified and status data is transmitted to the computer indicating that the update request has failed. The subsystem will send the original key-lock value to the computer upon demand. One alternative embodiment of the invention has means for designating a predetermined unlocked key value as indicative of the key-lock being unlocked.

Storage subsystem having a modifiable key-lock

A data storage system is described which provides for fault tolerance during execution of a media maintenance program on a selected track of nonvolatile data storage. Checkpoint data for the media maintenance program is stored in nonvolatile storage prior to writing control information on the selected track during the execution of the media maintenance program. The checkpoint data includes an address in the media maintenance program for resuming execution in the event that the media maintenance process is aborted. The checkpoint data is read from the nonvolatile storage area after media maintenance has been aborted by a fault, typically after power has been reapplied to the system. The execution environment for the media maintenance program is restored by storing data in the RAM of the controller which duplicates the control data needed by the particular segment of the media maintenance program which will be restarted. After the environment is restored, the execution of the media maintenance program resumes at the address in checkpoint data stored prior to writing the control data on the selected track.

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San Jose, CA, United States of America

Barrie N Harding