Fabric Manager Users Guide, Version 6.1, Revision A - QLogic

2–Advanced Fabric Manager Capabilities
Packet and Switch Timers
Multicast Spanning Tree Root
Multicast routing is performed by computing a spanning tree for the fabric. The
tree has a root switch and spans throughout the fabric to reach all of the switches
and Host Channel Adapters which are members of the multicast group.
The QLogic Fabric Manager allows the root of the spanning tree to be configured
using the Sm.Multicast.RootSelectionAlgorithm parameter.The SM’s
MinCostImprovement parameter can determine how much improvement is
needed before a new spanning tree root is selected. Disruption to in-flight
multicast traffic can be avoided or limited to cases where the fabric has changed
significantly enough to provide sufficient benefit to justify a change by using these
parameters.
The SM’s DB Sync capability synchronizes the multicast root between the master
and standby SMs. During SM failover the multicast root can be retained and limit
disruption to multicast traffic in flight.
Multicast Spanning Tree Pruning
A complete tree will unconditionally include all switches. When Host Channel
Adapters request to join or leave the multicast group the SM only needs to
program the switch immediately next to the Host Channel Adapter.
A pruned tree will omit switches which do not have Host Channel Adapters as
members of the group, as well as intermediate switches that do not need to be in
the group. A pruned tree will reduce multicast traffic internal to the fabric when
only a small subset of nodes are part of a given multicast group. The time to add
or remove Host Channel Adapters from the group can be significantly higher as
many intermediate switches may need to also be programmed for the group.
The default is a complete tree. This has been found to work very well in HPC
environments. Such environments typically have very little multicast traffic with the
vast majority of traffic being IPoIB ARP packets which need to be broadcast to all
nodes running IPoIB. The default allows IPoIB hosts to come up and down
quicker.
Packet and Switch Timers
Switch Timers
The InfiniBand standard allows for assorted timers and lifetimes to be set to avoid
unforeseen situations that can cause packets to be lost or progress to be stalled
causing widespread impacts from localized situations (For example, a hung
server, broken ISL, and so on). The SM allows these timers to be configured by
the adminstrator.
Every switch supports the following standard timers:
IB0054608-01 B 2-19