IBM 990 - Manual (Page 95)

Chapter 3. I/O system structure 83
possible to see any places where a control unit, or group of control units, have single
points of failure (SPOF); in this case, books and MBAs are of interest.
For the next step, use the CFReport for FC2400 along with the same IOCP statements
and repeat the availability option in the CMT. This will potentially show a different set of
SPOFs.
By comparing the two reports, you can determine if FC2400 is the right choice and what, if
any, other configuration changes will need to be made in conjunction with the install of
FC2400.
I/O port balancing across MBAs and books
At I/O definition time, the customer is able to select I/O ports for different paths of a multi-path
control unit that come from different I/O cards, different I/O domains (including different
eSTI-M cards and different STI links), different I/O cages, and different MBAs from different
books. This improves I/O throughput and system availability by avoiding single point of failure
paths.
Figure 3-7 shows a simplified example of multi-path device connectivity.
Figure 3-7 Balancing multi-path device connectivity example
Of course, this example assumes that there are enough I/O cards available for such
connectivity distribution, and this may not be true for all channel types on a given real
configuration. However, the overall goal is to avoid, as much as possible, connectivity single
points of failures.
2084-D32 CEC Cage
I/O Cage 1 I /O Cage 2
Book 0 Book 1
STIs
STI Links
MBA
0
MBA
1
MBA
2
MBA
0
MBA
1
MBA
2
Book 2 Book 3
MBA
0
MBA
1
MBA
2
MBA
0
MBA
1
MBA
2
Book 0
Book 3 Book 2
Book 1