Browse Prior Art Database

Preservation of Volume Integrity

IP.com Disclosure Number: IPCOM000051808D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 59K

Publishing Venue

IBM

Related People

Meritt, AS: AUTHOR

Abstract

In current data processing systems (Fig. 1) data is transferred betwee direct-access storage devices (DASDs) 10 and main storage facilities 12 in central host processing subsystems 14 via 1/0 channels 16 and I/0 control units 18. In the host system the data may be processed by one or more central processing units 20. The supervisory programs which control the host system may be adapted to maintain record logs of the integrity of volumes stored on the DASDs, e.g., to insure that I/0 data transfer requests are directed to appropriate volumes and to authorized or appropriate areas on such volumes.

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Preservation of Volume Integrity

In current data processing systems (Fig. 1) data is transferred betwee direct-access storage devices (DASDs) 10 and main storage facilities 12 in central host processing subsystems 14 via 1/0 channels 16 and I/0 control units
18. In the host system the data may be processed by one or more central processing units 20. The supervisory programs which control the host system may be adapted to maintain record logs of the integrity of volumes stored on the DASDs, e.g., to insure that I/0 data transfer requests are directed to appropriate volumes and to authorized or appropriate areas on such volumes.

A problem in this respect is that the integrity record maintained by the host system may be ambiguous or incorrect due to incomplete or faulty device status communications. For instance, a device end interruption intended to represent the mounting of a device may be incorrectly received or interpreted in the host system.

Usually, reception of a device-end interruption at times other than expected endings of data transfer operations is interpreted by the host system as representing the occurrence of one of several events:
(1) a response to a previously reported busy condition from a device which is no longer busy, or (2) a manual change of device status from not-ready to ready. The occurrence of a volume change is actually subject to interpretation as one species of not-ready to ready transition.

Accordingly, interpretation of each device-end interruption requires the host system to perform volume integrity verification whenever the possibility of a not- ready to ready transition occurs.

This ambiguity in the host interpretation of device-end could be eliminated by providing for more specific communication of status to the host system during interruptions. However, in such circumstances, error conditions which would cause the host system to fail to receive the device-end interruption would also cause any more specific status information to be lost.

A more efficient solution to this problem is the subject of this article. The device and control unit are adapted to maintain an integrity check indication relative to the host system and reject data transfer commands whenever a condition occurs in the device subsystem which is capable of altering volume or data integrity. The host and control unit are adapted to clear this check indication only by a Verify Read command which is subject to origination only by host supervisory control software.

As shown in Fig. 1, the control unit(s) associated with a device have lines 24, in each interface path 26 of connection to host system 14, for presenting an integrity check indication to that host.

As shown in Fig. 2, the signal associated with this check indication is also applied to logic circuits 42 in the control unit to cause the control unit to reject or ignore all data transfer commands initiated on the host side of the system until a V...