HP 376227-B21 - ProLiant InfiniBand 4x Fabric Copper Switch, User Manual

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• Routing internally within a switch (hops between switch chips)
• Routing between whole switches (hops between nodes). This is also referred to as routing between
“switch elements.”
Internal switch routing can be configured to provide the highest performance in passing traffic, and to
minimize the threat of congestion within the switch.
The Routing Process Overview
1. The Subnet Manager (SM) first discovers all the InfiniBand switch chips in the network.
2. The SM groups the internal switch chips within each chassis into a “switch element.”
3. The SM process continues until all the InfiniBand switches are grouped into “switch elements.”
4. After all the switch chips are grouped, the SM will route the switch elements according to the
routing algorithm discussed in “Minimum Contention, Shortest Path & Load Balancing Algorithm”
on page 6 .
5. The internal network of each InfiniBand switch is then routed based on the best algorithm for each
“switch element.”
Multiple Paths
The SM allows you to define the Logical Identifier Mask Control (LMC) value per subnet. The default
value of the LMC is 0, so by default only one Logical Identifier (LID) is assigned to each host port.
Once the LMC value has been assigned, the SM will route different paths for each LID associated with
the same host port. The result of these paths is based on the routing algorithm applied.
Understanding SM Routing Terms
The following terms are important to understand before distinguishing the various types of algorithms
that the Subnet Manager uses for routing:
Distance - Distance is defined as the number of hops (InfiniBand switches or “switch elements”)
between source and destination.
Contention - A contention is declared for every switch port on the path that is already used for routing
another LID associated with the same host port.
Minimum Contention, Shortest Path & Load Balancing
Algorithm
Minimum Contention, Shortest Path and Load Balancing is the algorithm that is used by default to route
between the “switch elements” and for routing between the internal InfiniBand switch chips
within each
“switch element.”
The following algorithm is used for the calculation:
1. The shortest path for each of the host ports is calculated.
2. Contention is calculated for all the available paths that are within the (shortest path + tolerance)
distance.
a.
The path with the least contention is selected.
b. If two paths have the same contention, the path with less distance is selected.
c.
If two paths have the same contention and the same distance, the port usage count is used to
provide load balancing over the two paths. The usage count is a measure of how many LIDs have
been configured to use that particular port.
Configuring Your Network For Optimal Routing
Create Equal Paths Between Switch Elements
It is recommended that InfiniBand switch elements be connected so that all paths between any pair of
switch elements are the same distance (i.e. same number of hops), if possible. This enables you to
obtain the optimal paths using the default tolerance of 0.