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Batching DASD Accesses in a Multi-User Environment

IP.com Disclosure Number: IPCOM000050194D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Nolta, AH: AUTHOR [+3]

Abstract

In accessing any one of a plurality of direct-access storage devices (DASDs) all outstanding access requests to a given DASD are batched together into a single chain of commands, including requests from all users. As each access work is completed, the respective user is notified for rapid data availability. The requests are sorted such that DASD accessor arm movements are optimized for minimizing seek distance. The DASD remains selected throughout the chain irrespective of the number of users having requests serviced by the chain.

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Batching DASD Accesses in a Multi-User Environment

In accessing any one of a plurality of direct-access storage devices (DASDs) all outstanding access requests to a given DASD are batched together into a single chain of commands, including requests from all users. As each access work is completed, the respective user is notified for rapid data availability. The requests are sorted such that DASD accessor arm movements are optimized for minimizing seek distance. The DASD remains selected throughout the chain irrespective of the number of users having requests serviced by the chain.

Referring to the figure, a plurality of users access DASD via a storage access control. For each user, a logical device control block (LDCB) is generated for each of the devices, as shown. Three LDCBs are associated with each physical device, allowing up to three users for simultaneous access to each DASD. Storage access control receives a plurality of user access requests and queues them by device, i.e., each DASD has a separate work queue. The storage access control scans the queue and decides on predetermined criteria which device to next access for satisfying user requirements.

For each device, the storage access control sorts the accesses for all users in accordance with the present position of the transducer on the DASD being addressed, and other criteria to minimize the number and durations of transducer motions minimal, usual minimum access programming may be used. Then, the range of accesses are selected for the device. This may be the entire queue or le...