IBM eServer zSeries 990 Technical Guide

Chapter 3. I/O system structure 79

Depending on the number of I/O slots plugged into the cage, there may be from one to seven

eSTI-M cards plugged into a z990 I/O cage. The eSTI-M card can be installed or replaced

concurrently.

STI-2 Extender card

The STI-2 Extender card (Feature Code 3992) takes the 2 GBps link from an MBA’s STI and

creates two secondary 333 MBps STI links, which are used to connect ICB-2 links. ICB-2 is

supported only for connection to G5/G6 servers.

The number of STI-2 Extender cards depends on the number of ICB-2 links in a configuration.

Usually, the number of STI-2 Extender cards is half the number of ICB-2 links, but for

availability reasons, two ICB-2 links are connected to two STI-2 Extender cards, each one

having one active ICB-2 link port.

The maximum number of STI-2 Extender cards in a z990 server is four cards, resulting in up

to eight ICB-2 ports. All of them can be installed in a single I/O cage. The STI-2 Extender card

can be installed or replaced concurrently.

STI-3 Extender card

The STI-3 Extender card (Feature Code 3993) takes the 2 GBps link from an MBA’s STI and

creates two secondary 1 GBps STI links, which are used to connect ICB-3 links.

The number of STI-3 Extender cards depends on the number of ICB-3 links in a configuration.

Usually, the number of STI-3 Extender cards is half the number of ICB-3 links, but for

availability reasons, two ICB-3 links are connected to two STI-3 Extender cards, each one

having one active ICB-3 link port.

The maximum number of STI-3 Extender cards in a z990 server is eight cards, resulting in up

to 16 ICB-3 ports. All of them can be installed in a single I/O cage. The STI-3 Extender card

can be installed or replaced concurrently.

3.2.3 Balancing I/O connections

The z990 server’s multi-book structure results in multiple MBAs; therefore, there are multiple

STI sets. This means that an I/O distribution over books, MBAs, STIs, I/O cages, and I/O

cards is desirable for both performance and availability purposes.

The STI links balancing across a book’s MBAs, I/O cages, and I/O cards is done by IBM at the

server’s initial configuration time. Follow-on upgrades of the initial server configuration,

including additional book(s) and/or I/O cage(s), may undo the balance of the original STI links

distribution.

The optional upgrade feature STI Rebalance (Feature Code 2400) can be requested at

upgrade configuration time to rebalance STI links across the new total number of books and

I/O cages. However, STI rebalancing is disruptive, requiring a server outage.

The processor I/O ports balancing across I/O cards, I/O cages, STI links, and a book’s MBAs

is done by the customer at I/O definition time. This is done by either the use of the CHPID

Mapping Tool to assign CHPIDs to PCHIDs, or manually by assigning installed PCHIDs to

CHPIDs. The use of the CHPID Mapping tool is strongly recommended.

The balancing may also be affected by the STI Rebalance feature (FC 2400) after a server

upgrade.

80 IBM ^ zSeries 990 Technical Guide

STI links balancing across books and MBAs

Figure 3-4 shows a 2084-B16 server’s initial configuration example with two fully populated

I/O cages (seven I/O domains on each one).

Figure 3-4 2084-B16 initial configuration example

The 2084-B16 server has two books in the CEC cage. The STI links are distributed across

books, MBAs, and I/O cages, as a result of the initial server configuration balancing.

Nearly the same number of STIs of each book’s MBA are used and spread across the two I/O

cages, resulting in the best STI link distribution for both performance and availability.

Figure 3-5 on page 81 shows an upgrade from this 2064-B16 server to a model D32,

maintaining the same I/O cages and I/O cards.

2084-B16 CEC Cage

I/O Cage 1 I/O Cage 2

Book 0

Book 1

STIs

I/O Domains

STI Links

I/O Cards

MBA

0

MBA

1

MBA

2

MBA

0

MBA

1

MBA

2