Browse Prior Art Database

Executing a Reserve Release on Sub Device Data Increments in a DASD System

IP.com Disclosure Number: IPCOM000087443D
Original Publication Date: 1977-Jan-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Brock, RL: AUTHOR [+3]

Abstract

This article describes the use of a locking table stored on a direct-access storage device (DASD) to control reserve/release (R/R) to sub-device data increments. More particularly, it covers a method for executing R/R on sub-device increments stored in DASD, comprising the steps of (a) receiving a request to R/R, a sub-device increment, from a host/channel, (b) updating a reservation table of data addresses stored on the device, the table itself being device stored, and (c) controlling access to the reserved increment on the device, as a function of lookup of the reservation table, in response to any access requests.

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Executing a Reserve Release on Sub Device Data Increments in a DASD System

This article describes the use of a locking table stored on a direct-access storage device (DASD) to control reserve/release (R/R) to sub-device data increments. More particularly, it covers a method for executing R/R on sub- device increments stored in DASD, comprising the steps of (a) receiving a request to R/R, a sub-device increment, from a host/channel, (b) updating a reservation table of data addresses stored on the device, the table itself being device stored, and (c) controlling access to the reserved increment on the device, as a function of lookup of the reservation table, in response to any access requests.

Reserve/release signify processes for causing a device to be exclusively allocated to a host/device communication path, i.e., channel (i) and CPU (j). It is an object of the above method to reduce the locking level to less than the disk pack in order to reduce the table lookup access time. The table is stored under the fixed head portion of the DASD.

Referring to Fig. 1, there is shown a string of drives 0, 1, 2, a controller, and a string switch coupling control units 0 and 1. Access to any of the drives by CPU 0-3 is through control unit 0 and the string switch over path A. Similarly, access by any of the CPUs 4-7 is through control unit 1 and the string switch over path
B.

Referring now to Fig. 2, there is shown a reservation table of the sub-device data increment addresses stored on the device. When a CPU needs to reserve space on a DASD, it issues a Cylinder Reserve channel command word (CCW). The control unit reads the cylinder reservation table on the...