Managing Superdome Complexes: A Guide for HP-UX System Administrators

Planning Superdome Configurations
Rules and Guidelines for Configuring a Complex
Appendix A324
Recommendations for Cabling Crossbar Controllers
(XBCs)
Before you go on, read:
• “What is a Partition?” on page 298.
• “What is a Cell?” on page 303.
• “What is an XBC (Crossbar Controller)?” on page 312:
- “Crossbar Connections” on page 314.
Other terms and concepts:
• 32-way, 64-way-capable system: see“What is a CPU Cabinet?” on
page 299.
• CPU cabinet: see “What is a CPU Cabinet?” on page 299.
• Complex: see“What Is a Complex?” on page 292.
When Do You Need To Think about Cabling?
Use this section whenyou are creating a new complex, or adding a CPU
cabinet to a complex (or removing a CPU cabinet).
The crossbar controllers (XBCs) within a CPU cabinet are connected to
each other by one direct connection which is not configurable - it's always
there. You need to decide whether to use U-Turn or Cross-Flex cabling
to connect the two remaining ports; see “Crossbar Connections” on page
314 for explanations and diagrams.
Guidelines for Performance
• Always configure a 32-way-capable system with U-Turn.
U-Turn provides twice the bandwidth between XBCs in the same
cabinet.
• Always configure a 64-way-capable-system with Cross-Flex.
Cross-Flex increases bandwidth between cabinets in a
64-way-capable-system, providing the best performance for large
partitions.
U-Turn is not recommended in a 64-way-capable-system because it
would reduce the bandwidth between the cabinets; for example, there
would be no direct connection between XBC 4 and XBC 8 in a U-Turn
64-way-capable-system, resulting in two hops for any communication
between cells on these crossbars.