Browse Prior Art Database

Scheduling Memory Resources in a Virtual Environment

IP.com Disclosure Number: IPCOM000082414D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Waddell, JM: AUTHOR [+2]

Abstract

In a multicomputer shared-memory subsystem, such as those employing disk memory units, each host CPU may have its own address independent space of virtual disk drives, for example, 0-32 virtual units (VU's). Host A may have virtual unit 01 which appears to the host as a disk drive, actually, with data portions recorded on real disk unit A in tracks 0-40 and another portion of the virtual unit 01 being recorded in tracks 50-53 of real disk B.

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Scheduling Memory Resources in a Virtual Environment

In a multicomputer shared-memory subsystem, such as those employing disk memory units, each host CPU may have its own address independent space of virtual disk drives, for example, 0-32 virtual units (VU's). Host A may have virtual unit 01 which appears to the host as a disk drive, actually, with data portions recorded on real disk unit A in tracks 0-40 and another portion of the virtual unit 01 being recorded in tracks 50-53 of real disk B.

Similarly, a second CPU may have a virtual unit 14 with a portion of its data recorded on real disk B in tracks 0-10 and another portion thereof recorded on disk drive C on tracks 25-43. Since the hosts may be operating independent of one another, both hosts could simultaneously request access to the virtual units 01 and 14, respectively, hence, requiring simultaneous access to disk drive B.

When such a contention occurs, the principles set forth in U. S. Patent 3,688,274 are employed to resolve the contention. The VU's which yield to a first VU, are stored for generating a later DVCEND signal to the appropriate host on a first in-first out (FIFO) basis. Each of the yielding VU's result in a command retry to the host CPU for the respective VU's. For example, if there are 14 hosts sharing a given real disk drive, there can be up to 13 command retries outstanding at each given instant.

Storage of the VU's which yield in a command retry environment is within the disk controlle...