Chapter 1. IBM zSeries 990 overview 7
Draft Document for Review April 7, 2004 6:15 pm 6947ch01.fm
1.3.5 Physical Channel IDs (PCHIDs) and CHPID Mapping Tool
A z990 can have up to 1024 physical channels, or PCHIDs. In order for an operating system
to make use of that PCHID, it must be mapped to a CHPID within the IOCDs. Each CHPID is
uniquely defined with an LCSS and mapped to an installed PCHID. A PCHID is eligible for
mapping to any CHPID in any LCSS.
The z990 CHPID Mapping Tool (CMT) provides a method of customizing the CHPID
assignments for a z990 system to avoid attaching critical channel paths to single points of
failure. It should be used after the machine order is placed and before the system is delivered
for installation. The tool can also be used to remap CHPIDs after hardware upgrades that
increase the number of channels.
The tool maps the CHPIDs from an IOCP file to Physical Channel Identifiers (PCHIDs) which
are assigned to the I/O ports. The PCHID assignments are fixed and cannot be changed.
A list of PCHID assignments for each hardware configuration is provided in the PCHID Report
available when z990 hardware is ordered. Unlike previous zSeries systems, there are no
default CHPID assignments. CHPIDs are assigned when the IOCP file is built. When
upgrading an existing zSeries configuration to z990, CHPIDs can be mapped by importing the
IOCP file into the z990 CHPID Mapping Tool.
1.3.6 Spanned channels
As part of the z990 LCSS, the Channel Subsystem is extended to provide the high-speed,
transparent sharing of some channel types in a manner that extends the MIF shared channel
function. Internal Channel types such as HiperSocket (IQD) and Internal Coupling Channels
(ICP) can be configured as “spanned” channels. External channels such as FICON channels,
OSA features, and External Coupling Links can be defined as spanned channels. Spanned
channels will allow the channel to be configured to multiple LCSSs, thus enabling them to be
shared by any/all of the configured logical partitions, regardless of the LCSS in which the
partition is configured.
Note: Spanned channels are not supported for ESCON channels, FICON conversion
channels (FCV), and Coupling Receiver links (CBR, CFR).