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

2–Advanced Fabric Manager Capabilities
Fabric Unicast Routing
Figure 2-3. Sample Cabling for Part of a 2D Mesh with 2 ISLs in Each Direction
When routing a torus fabric, DOR uses 2 Virtual Lane (VL)s on ISLs (to avoid
credit loops) and uses 2 dimensions Service Level (SL)s.
The QLogic Fabric Manager’s SM implements an augmented DOR algorithm
which also handles fabric disruptions for mesh and torus topologies. To handle
fabric disruptions, an additional VL and SL is used for an Up/Down routing
algorithm which can route around the failure. Such routing around failures may be
non-optimal, but it will be credit loop free. The Up-Down routing algorithm also
uses an additional LID per Channel Adapter, therefore for dor-updown the LMC of
the Channel Adapters will be 1 (2 LIDS per Channel Adapter) or greater. A Mesh
requires a minimum of 2 VLs per ISL and a Torus requires a minimum of 3 VLs per
ISL. Both a Mesh and a Torus require only 1 VL for Host Channel Adapter to
Switch links. Refer to Appendix D for a table summarizing the various
combinations of Mesh/Torus and vFabric/QoS along with the SL/VL requirements
for each combination.
Since the InfiniBand standard is limited to 16 SLs, there is a limit of 3 dimensions
for Torus fabrics with disruption handling (for a total of 9 SLs). Mesh fabrics do not
have this limitation.
2-6 IB0054608-01 B