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

1–Overview of the QLogic Fabric Manager Suite
SM Algorithms & Features
SM Algorithms & Features
Routing Algorithms in the SM
The primary routing algorithm selects, for every pair of nodes in the fabric, the
quickest path available. In the case where there is more than one path available,
load-balancing of the paths occurs over the available ports at each switch to get
an even distribution of traffic over the fabric. Refer to “Routing Algorithm” on
page 2-3 for detailed information.
Spine-first routing is an optional feature that, when enabled, will favor paths that
route through a chassis, rather than a path that exits and then re-enters a chassis.
This helps eliminate cycles (for example, credit loops) on fabrics where such
routes are possible. Refer to “Shortest Path” on page 2-3 for more information.
LID Mask Control (LMC)
The LMC feature provides a method for assigning multiple addresses, local
identifiers (LIDs) to a single physical port. This allows for multiple paths through
the fabric to be configured between a single pair of nodes. When enabled, the
routing algorithm will attempt to ensure that these paths are placed on unique
hardware when possible in order to reduce disruption in the case of switch failure.
Each end-node port will have 2 LMC address LIDs. Refer to “LMC, Dispersive
Routing and Fabric Resiliency” on page 2-8 for detailed information.
Multicast Group Support
Multicast groups are used to direct one-to-many and many-to-many traffic. Nodes
subscribe to multicast groups by issuing requests to the SM. The user may use
SM CLI commands to manage multicast groups. Refer to “Fabric Multicast
Routing” on page 2-16 for detailed information.
Fabric Manager’s InfiniBand Subnet Manager
The QLogic Fabric Manager implemented a complete InfiniBand Subnet Manager
(SM). The SM is responsible for monitoring, initializing and configuring the fabric.
One of the critical roles of the SM is the initialization and configuration of routing
tables in all the switches. The QLogic Fabric Manager’s SM supports a variety of
routing algorithms which will be discussed in detail later in this guide. Among the
capabilities are:
• Support for a wide range of fabric topologies, including Fat Tree, Clos
network, Mesh/Torus and various irregular topologies
• Support for assigning multiple LIDs to end nodes and the carefully balanced
programming of alternate routes through the fabric for use by dispersive
routing, load balancing and failover techniques by various upper level
protocols (ULP).
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