IBM eServer zSeries 900 Technical Guide

Chapter 3. Connectivity 83

򐂰 Better manage the establishment of logical paths

3.1.6 Channel planning for availability

As a general recommendation, multiple path connections should have their paths spread

across channel cards that are on different MBAs from different processor clusters, avoiding

single points of failure. The CHPID Mapping Tool helps to establish the best I/O availability for

an initial z900 configuration (see Appendix E, “CHPID Mapping Tool” on page 285). However,

currently the CHPID mapping tool only works with z900

initial configurations as shipped by

manufacturing, and does not help on future upgrades.

The z900 Configurator rules also help single point of failure avoidance, as described in the

following examples using the ISC-3 and ESCON 16-port channel cards.

ISC-3 channel cards

ISC-3 channels use ports on the ISC Daughter (ISC-D) card. Each ISC-D card has 2 ports

and is installed on the ISC Mother (ISC-M) card, which resides on an I/O slot. Up to two

ISC-D cards can be plugged on an ISC-M card.

If you order only two ISC-3 coupling links, a single 2-port ISC-D card and one ISC-M card

would be enough to provide this number of links. However, the configuration will be shipped

with two 2-port ISC-D cards, each one plugged into a different ISC-M card, which are on

different MBAs. Each ISC-D card will have only one port enabled via LIC-CC. The resulting

configuration has

doubled the installed infrastructure required by the connectivity needs. This

also allows future ISC-3 link upgrades via LIC-CC, since up to two more ports can be

concurrently enabled.

It is also possible to

plan-ahead a future I/O configuration, allowing concurrent channel

upgrades even when additional infrastructure, like frames, I/O cages, or cards, would be

required.

Using the previous example, if more than the two unused ISC-3 link ports are required for

planned upgrades, more ISC-M cards will be required. If there is no I/O slot available on an

existing zSeries I/O cage, one more zSeries I/O cage must be installed to accommodate this

additional ISC-M card. This new I/O cage may even require a Z frame. ISC-M cards can be

concurrently installed, but an I/O cage or frame installation is disruptive. This results in a

disruptive ISC-D card installation. Using the planned upgrades information on the plan-ahead

concurrent conditioning process results on the pre-installation of the required I/O cages and

frames in the initial server configuration, allowing a nondisruptive upgrade. (Note: in this

particular case of ISC-3 upgrades, the additional ISC-M cards required by the target

configuration will also be included on the initial configuration.)

ESCON 16-port channel cards

ESCON 16-port channel cards are always shipped and installed in pairs to achieve the

required amount of ESCON channels. The cards of a channel card pair are connected to

different MBAs, avoiding single points of failure.

Up to 15 ports per channel card can be used. ESCON ports are enabled via LIC-CC in

increments of four ports, which are spread across different channel cards. When there are

ports available, concurrent ESCON channel upgrades can be done with no hardware

changes.

So, as an example, if a configuration has only 4 ESCON channels, there will be 2 ESCON

16-port channel cards installed, each one having 2 ESCON ports enabled via LIC-CC. Then if

four more ESCON channels are ordered, LIC-CC enables two more ESCON ports on each

channel card.