IBM eServer zSeries 900 Technical Guide

84 IBM eServer zSeries 900 Technical Guide

When the number of available ESCON ports (up to 15 per channel card) is not sufficient to

satisfy a channel upgrade, them more pair(s) of ESCON 16-port channel cards are shipped.

in the previous example, the two installed ESCON channel cards can accommodate up to 28

ESCON channels (not 30, since they must be enabled in groups of 4 ports). After that, if four

more channels are required, then

two more ESCON 16-port channel cards are shipped, each

one having two ports enabled. The two initial ESCON channel cards ports remain

unchanged.

3.1.7 Configuration guidelines and recommendations

When configuring devices with multiple paths to the same server, select any of the channel

paths from any I/O card that:

򐂰 Are available on the CPC you are defining

򐂰 Are the correct type (ESCON, FICON, etc.) to meet the control unit, coupling facility, or

network attachment requirements

򐂰 Satisfy the rules regarding the mixing of channel types

However, for maximum availability of the device, OSA network, or coupling facility on z900

servers, you should consider the following guidelines:

򐂰 For systems with multiple I/O cages, distribute paths across the I/O cages. When choosing

which STIs to use in different cages, follow the guidelines in the following bullet.

򐂰 For systems with multiple STIs, distribute paths across the STIs.

This is also recommended for optimum performance of your most heavily-used I/O

devices.

When choosing the STIs to use, either from different I/O cages or from the same I/O cage,

consider using a combination of STIs from MBA cluster 0 and MBA cluster 1 to critical I/O

devices. Refer to your CHPID Report to determine which STI links belong to which MBA

cluster. If you have multiple paths to the device and multiple domains available that have the

correct channel type, spreading the paths across all the MBAs is also advisable.

Connecting your critical devices this way will ensure access to those devices while running in

a degraded mode. In the unlikely event of a Memory Bus Adapter (MBA) or related failure, you

may be able to take advantage of the Partial I/O Restart function.

When configuring ICB or coupling CHPIDs for the same target CPC or coupling facility, use a

combination of STIs from MBA cluster 0 and MBA cluster 1. Use ICBs from different STI-H

cards. This will ensure paths are from different MBA clusters and will allow for continued

connectivity if Partial I/O Restart is used.

򐂰 For the zSeries I/O cage (FC 2023):

If you define multiple paths from the same STI, distribute paths across different channel

cards. Also, if you define multiple coupling facility channels to the same coupling facility or

the same operating system image, distribute paths across different coupling facility

channel adapter cards or different ISC Daughter (ISC-D) cards.

򐂰 For the compatibility I/O cage (FC 2022):

When choosing different STIs from a compatibility I/O cage, try to pick STIs from different

STI-H cards.

– If you define multiple paths from the same STI, distribute paths across different I/O

cards controlled by different CHAs.