Browse Prior Art Database

SUPPORTING PARALLEL ACCESS VOLUMES USING ADJUNCT CHANNEL SUBSYSTEMS

IP.com Disclosure Number: IPCOM000013353D
Original Publication Date: 2000-Nov-20
Included in the Prior Art Database: 2003-Jun-18
Document File: 1 page(s) / 50K

Publishing Venue

IBM

Abstract

The S/390 I/O architecture provides for up to 64K subchannels to be

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  SUPPORTING PARALLEL ACCESS VOLUMES USING ADJUNCT CHANNEL SUBSYSTEMS

  The S/390 I/O architecture provides for up to 64K subchannels to be
defined to a single operating system. However, today we see control units
being built with a very large number of devices; it is possible to have
control units which support multiple subchannels for a single device,
referred to as "parallel access volumes" (PAVs)1. It is easy to see how
the 64K subchannels could be exhausted when multiple subchannels are used
for devices. Subchannels represent 2 things: (1) a configured volume, and
(2) the anchor for active work to that configured volume. In the case of
devices with PAVs, only 1 subchannel is needed to represent the
configured volume, and the additional subchannels are needed only as
anchors for active work. By providing a means to separate the additional
subchannels used for PAVs from the subchannels representing the
configured volumes, the number of volumes which can be configured to the
system is maximized. The most straightforward way to provide more
subchannels is to simply expand all the fields relevant to subchannel
addressing; this would include the subchannel number used for many
instructions, the subchannel number returned on I/O interrupts, etc.
Since the device number field is also limited to 64K things, it would
also have to be expanded, impacting software, customers, etc. However,
this approach represents a very disruptive change. Creating an Adjunct
Channel Subsystem (ACS)
to contain subchannels for the PAVs minimizes the
disruption by keeping...