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

2–Advanced Fabric Manager Capabilities
Fabric Change Detection
During the analysis and reprogramming process the fabric may still be changing.
In this case errors may occur. When more than the set SweepErrorsThreshold
parameter of non-recoverable errors (such as a device going offline mid sweep)
occur during a single sweep, the SM will abandon the sweep and start it over, to
obtain a complete and accurate view of the fabric. The SM will not abandon the
sweep more than the set SweepAbandonThreshold parameter of consecutive
times, after which it will do the best it can. This helps to handle a fabric which is
constantly changing, such as a fabric with an unstable link.
Similarly, if a port issues more than the TrapThreshold number of changes per
minute, the SM considers the link unstable and will disable the port, removing it
from the fabric, preventing any traffic to be routed over it.
Additionally the Suppress1x configuration parameter allows the SM to disable
1x links, removing low speed and low quality links from the fabric. All hardware
available from QLogic is capable of 4x or more. 1x links typically represent
devices with partially bad cables or hardware.
Tolerance of Slow Nodes
In rare cases, nodes under a heavy load, such as when running high stress MPI
applications, will be slow to respond to SM sweeps. To avoid disrupting
application runs, the SM can be configured using NonRespTimeout and
NonRespMaxCount to be more tolerant of such devices and assume their
capabilities have not changed since the last successful sweep.
The trade-off in increasing the tolerance is that loss of nodes will be detected
much slower. Typically this capability is only relevant to Host Channel Adapters.
The risk in this feature mainly applies to nodes which hang but keep their link up
so that the neighbor switch does not report a port state change.
NOTE:
When using OFED, it is recommended to set RENICE_IB_MAD=yes, this
will ensure rapid responses by the SMA and actually reduce overhead by
avoiding the cost of retries. This option is enabled by default when using
QLogic OFED+
Multicast Denial of Service
In rare cases, nodes send excessive multicast creates/deletes several times a
second for the same group causing continuous SM sweeps. To stop the
continuous SM sweeps, Multicast (MC) Denial of Service (DOS) can be set up in
the configuration file to monitor the MC DOS Threshold, set up the interval of
monitoring, and either bounce the port or disable the port.
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