Multiple Logical Channel Subsystems (LCSSs)

Published 20 May 2003, updated 09 December 2004

Authors: Bill White


The z990 and z890 servers provide the ability to have more than 256 CHPIDs in the system by the introduction of the Logical Channel Subsystem. This is a logical replication of CSS facilities (CHPIDS, control units, subchannels, and so on). This enables a balanced system structure between the server’s capability and the I/O capability. The LCSS for the z990 or z890 server introduces significant changes to the I/O configuration. This Technote provides a pictoral view of multiple LCSSs.


A pictorial view of a z990 or z890 server with multiple LCSSs is shown in the following figure. Two LCSSs are defined (0 and 1). Each LCSS has three LPARs, with their associated MIF Image Identifiers.

In each LCSS, the CHPIDs can be shared across all LPARs. The CHPIDs in each LCSS are mapped to their designated PCHIDs. For ease of management, it is strongly recommended that HCD and the CHPID Mapping Tool (CMT) be used to build and control your z990 or z890 input/output configuration definitions.

Special Notices

This material has not been submitted to any formal IBM test and is published AS IS. It has not been the subject of rigorous review. IBM assumes no responsibility for its accuracy or completeness. The use of this information or the implementation of any of these techniques is a client responsibility and depends upon the client's ability to evaluate and integrate them into the client's operational environment.

Follow IBM Redbooks

Follow IBM Redbooks