International Business Machines Corporation

Lloyd R Shipman, Jr

Brent Cameron Beardsley

John Richard Paveza

Chan Y Ng

Steven D Gerdt

Barrie N Harding

Dennis R Escola

Joseph S Hyde, Ii

Joseph S Glider

Eugene P Hefferon

Vernon John Legvold

James C Chen

Gary Eugene Morain

Kenneth R Lynch

Paul W Hunter

Joel H Cord

Jesse I Stamness

Carol Santich Michod

Susan Marie Wethington

Janet S Anglin

Christ J Xydes

Philip K Chai

Stephen W Schimke

A system and method for reducing device wait time in response to a host initiated write operation modifying a data block. The system includes a host computer channel connected to a storage controller which has cache memory and a nonvolatile storage buffer in a first embodiment. An identical system makes up the second embodiment with the exception that there is no nonvolatile storage buffer in the storage controller of the second embodiment. The controller in either embodiment is coupled to a cache storage drawer containing a plurality of DASD devices for implementing a RAID parity data protection scheme, and for permanently storing data. The drawer has nonvolatile cache memory which is used for accepting data destaged from controller cache. In a first embodiment, no commit reply is sent to the controller to indicate that data has been written to DASD. Instead a status information block is created to indicate that the data has been destaged from controller cache but is not committed. The status information is stored in directory means attached to the controller. The system uses this information to create a list of data which is in the state of Not committed. In this way data can be committed according to a cache management algorithm of least recently used (LRU), rather than requiring synchronous commit which is inefficient because it requires waiting on a commit response and ties up nonvolatile storage space allocated to back-up copies of cache data. In a second embodiment, directory means attached to the controller stores information about status blocks that may be modified or unmodified. The status information is used to eliminate wait times associated with waiting for data to be written to HDAs below.

Performance enhancement system and method for a hierarchical data cache

The present system may be utilized to minimize access performance penalties in memory subsystems which utilize redundant arrays of disk memory devices. Redundant arrays of disk memory devices provide levels of reliability which are not available with single storage devices; however, the redundancy carries with it an access performance degradation due to the requirement that such systems write data segments and parity elements to the array each time an application updates data within the system. A large nonvolatile cache is therefore provided in association with a redundant array of disk memory devices. Each time a data segment is written or read the data segment is staged from the array to the nonvolatile cache, if the data segment is not already within the cache. Additionally, if the operation is an update, a parity element associated with the data segment to be updated is also staged to the cache with the existing data segment content. An updated parity element is then calculated based upon the updated data, the existing data and the existing parity element. Data segments and associated parity elements are then maintained in the cache for future reading and updates until the number of updated data segments within the cache exceeds a predetermined value. Thereafter, selected data segments and associated parity elements are destaged from the cache to the array based upon a 'Least Recently Utilized' (LRU) or 'minimum seek' algorithm.

Method and system for enhanced data management efficiency in memory

A fault tolerant disk storage subsystem which includes a multipath dynamically alterable hierarchical arrangement of storage device controllers. Multiple storage device controllers are provided which are each adapted to emulate a storage device and which each include a cache memory which has multiple data input ports and multiple data output ports. A processing element within the storage device controller is utilized to selectively interconnect particular data input ports with selected data output ports to provide multiple paths within the storage device controller. An interconnection is then provided for coupling a data output port of one or storage device controller with a data input port of one more alternate storage device controllers which emulate storage devices, creating an alterable hierarchical arrangement of storage device controllers. Storage devices are then coupled to each of the lowest levels of the hierarchical arrangement of storage device controllers. As the storage device controllers may very in type and capability, various combinations of access speed and redundancy may be provided.

Fault tolerant data storage subsystem employing hierarchically arranged

The present application may be utilized for enhanced maintenance of data stored on storage media within a data processing system storage subsystem. Data to be stored is first subdivided into multiple blocks and subblocks, segments or tracks. Each subdivision of data is then analyzed and appropriate logical Error Correction Codes (ECC) are calculated and inserted into the data at selected locations to permit certain data errors to be corrected by subsequent processing. Thereafter, the data and associated logical Error Correction Codes (ECC) are then coupled to a head/disk assembly within a storage subsystem. A physical Error Correction Code (ECC) logic circuit is then utilized to analyze the data and logical Error Correction Codes (ECC) and appropriate physical Error Correction Codes (ECC) are then calculated and inserted into the data at selected locations in response to the storage of the data and logical Error Correction Codes (ECC) within the storage media. Maintenance of the storage media and data may then be separately accomplished utilizing independent logical and physical Error Correction Code (ECC) circuits which operate separately upon the logical and physical Error Correction Codes (ECC) wherein media defects will not necessarily result in a loss of all data present within the defective media segment.

Method and system for separate data and media maintenance within direct

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

The present invention is a controller and a method for its use in a disk data storage and retrieval system. The controller is of the type which associates a file mask with a sequence of commands. The controller has means for executing a critical-section-start (CSS) command received from the host computer which indicates to the controller that a critical sequence of commands will follow and places the controller in a critical sequence mode (CS mode). The controller has means for executing a critical-section-end (CSE) command which indicates the end of the commands. While in the CS mode the controller checks the file mask for each command received and refuses to execute selected commands which are not associated with predetermined values of the file mask (CS file masks). A program running on the host computer sends the controller a command establishing a CS file mask and the CSS command, then the program sends one or more sequences of critical commands to the controller. After the critical commands have completed successfully, the program sends the CSE command which returns the controller to the normal operating mode. If the critical commands fail then appropriate error recovery is performed while the controller is in the CS mode. The CS mode is used in conjunction with CS file masks to effect limitation of access to the disk system while critical commands are executing. More particularly the controller is used to perform concurrent media maintenance wherein media maintenance is performed on a suspect track while the user data formerly on that track is fully accessible by virtue of being copied to an alternate track.

Method and apparatus for executing critical disk access commands

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.

Disk storage system with fault tolerant media maintenance

A data processing system includes a plurality of host systems and peripheral subsystems, particularly data storage subsystems. Each of the data storage subsystems includes a plurality of control units attaching a plurality of data storage devices such as direct access storage devices (DASD) for storing data on behalf of the various host systems. Each of the control units have a separate storage path for accessing the peripheral data storage devices using dynamic pathing. The storage paths can be clustered into power clusters. Maintenance personnel acting through maintenance panels on either the control units or the peripheral data storage devices activate the subsystem to request reconfiguration of the subsystem from all of the host systems connected top the subsystem. The host systems can honor the request or reject it based upon diverse criteria. Upon each of the host systems approving the reconfiguration, the subsystem 13 is reconfigured for maintenance purposes. Upon completion of the maintenance procedures, a second reconfiguration request is sent to the host systems for causing quiesce devices to resume normal operations.

Device initiated partial system quiescing

Growing community of inventors

San Jose, CA, United States of America

Lloyd R Shipman, Jr