Browse Prior Art Database

Guaranteeing Data Path Integrity

IP.com Disclosure Number: IPCOM000048873D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Videki, ER: AUTHOR

Abstract

A peripheral subsystem connected to a utilization system having a plurality of host computers has a pair of control units CU0 and CU1, each of which has channel adapters CAl through CA4 and a pair of device adaptors DA0 and DA1. The device adaptors attach any one of a plurality of tape recorders, disk recorders, bubble memories, and the like, through either one of the control units to the utilization system. The crossed arrows intermediate the control unit symbols indicate that any of the channel adapters in either control unit can communicate with the buffer in either control unit. Accordingly, a CA3 of CU0 can utilize segment T of the buffer of CU1 for communicating with a given device. In e similar manner, CA2 of CU1 can utilize segment A of buffer of CU0 to communicate with another device.

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Guaranteeing Data Path Integrity

A peripheral subsystem connected to a utilization system having a plurality of host computers has a pair of control units CU0 and CU1, each of which has channel adapters CAl through CA4 and a pair of device adaptors DA0 and DA1. The device adaptors attach any one of a plurality of tape recorders, disk recorders, bubble memories, and the like, through either one of the control units to the utilization system. The crossed arrows intermediate the control unit symbols indicate that any of the channel adapters in either control unit can communicate with the buffer in either control unit. Accordingly, a CA3 of CU0 can utilize segment T of the buffer of CU1 for communicating with a given device. In e similar manner, CA2 of CU1 can utilize segment A of buffer of CU0 to communicate with another device. Utilization of the buffers by the two control units can vary depending upon the relationship of the processes in the utilization system and the device activity. When the data transfers being effected by either of the control units between the utilization system and the plurality of selected devices causes that control unit buffer to be full, then a device may be reassigned to another control unit for balancing the activity between the two control units.

This load balancing is achieved by using threshold detectors of activity indicators of diverse types. For some secure processes, it may be desired to inhibit a portion of the load balancing activity such that it can be guaranteed that a device of the backing store will always communicate through a segment of the buffer of CU1, while a second device will always communicate through the buffer of CU0. Accordingly, each of the buffer segments has a directory (not shown) which includes a pin bit P which signifies that the allocation of the segment to a device cannot be changed through load balancing activity. As shown, segments A and M, respectively, of CU0 and CU1 are pinned (P). Pinning the segments prevents transferring the device to which they are allocated to the other control unit. Therefore, for a specific set of two-device allocations to the buffer, such as A and M, the buffering for each of the backing store devices will always be maintained in those separate control units.

The pinning is achieved by so-called mode set command. A mode set channel command, transferred from the utilization system to either of the control units, contains a single byte of mode control data. The function before pinning in a preferred form are id effect only for the channel commands following the mode set. If no mode set command has been received specifying pinning, then a ...