Chapter 3. I/O system structure 79
Draft Document for Review April 7, 2004 6:15 pm 6947ch03.fm
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 GB/sec link from an MBA’s STI
and creates two secondary 333 MB/sec STI links, which are used to connect ICB-2 links.
ICB-2 are 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 4 cards, resulting in up to
8 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 GB/sec link from an MBA’s STI
and creates two secondary 1 GB/sec 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 8 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.