Browse Prior Art Database

Unconditional Reserve

IP.com Disclosure Number: IPCOM000086150D
Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Behman, SB: AUTHOR

Abstract

A channel command word to override a lock between a storage control unit and a string of direct access storage devices is described.

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Unconditional Reserve

A channel command word to override a lock between a storage control unit and a string of direct access storage devices is described.

As is well known, IBM system 360 or 370 controls access storage systems such as Direct Access Storage Devices (DASD) through a system of commands communicated from the computer to some type of device manager, using a system of instructions called Channel Control Words (CCW). There exists a "reserve" CCW which absolutely prohibits access to a device through any path save that through which the reserve command was given. The intent of the reserve CCW was to prevent simultaneous use of the same device by two independent computers, when either of the computers might have control of a file of information stored in the device in some partial state of "correctness".

The effect of the CCW was satisfactory except in the case of malfunction, i.e., when some part of the path used for the reserve was unavailable for the release of the device/computer interface. When the reserve path was unavailable, all paths were prohibited access. Prohibition, while creating certain difficulties, is preferable to unconstrained access such as might be provided on a time-out of the reserve status.

Desirable solutions permit access through an alternate path when the computer driving the path possesses sufficient programming/data a priori to avoid disrupting the data file. In DASD's such as the 3330, the device controller or "A-Box" exhibits...