Dell PowerConnect Brocade 300 Fabric OS Administrator's Guide v7.1.0 - Page 389

Excluding a port from bottleneck detection 13 • You want greater-than-default (sub-second) latency sensitivity on your fabric, so you set sub-second latency criterion parameters at the time you enable bottleneck detection. • You want to reduce the number of alerts you are receiving about known latency bottlenecks in the fabric, so you temporarily decrease the sub-second latency sensitivity on these ports. • You have a latency bottleneck on an ISL that is not at the edge of the fabric. The sub-second latency criterion parameters are always applicable. These parameters affect alerts and, even if alerting is not enabled, they affect the history of bottleneck statistics. The sub-second latency criterion parameters are the following, with default values in parentheses: • -lsubsectimethresh (0.8) is similar to the -lthresh alerting parameter, except on a sub-second level. The default value of 0.8 means that at least 80% of a second must be affected by latency for the second to be marked as affected. • -lsubsecsevthresh (50) specifies the factor by which throughput must drop in a second for that second to be considered affected by latency. The default value of 50 means that the observed throughput in a second must be no more than 1/50th the capacity of the port for that second to be counted as an affected second. 1/50th of capacity means 2% of capacity, which means 98% loss of throughput. Sub-second latency criterion parameters apply only to latency bottlenecks and not congestion bottlenecks. When you enable bottleneck detection, you can specify switch-wide sub-second latency criterion parameters. After you enable bottleneck detection, you can change the sub-second latency criterion parameters only on a per-port basis. You cannot change them on the entire switch, as you can with alerting parameters, unless you disable and then re-enable bottleneck detection. Changing the sub-second latency criterion parameters on specific ports causes an interruption in the detection of bottlenecks on those ports, which means the history of bottlenecks is lost on these ports. Also note the following behaviors if you change the sub-second latency criterion parameters: • Traffic through these ports is not affected. • History of latency bottlenecks and congestion bottlenecks is lost on these ports. Other ports are not affected, however. • The interruption occurs whether you set or clear per-port overrides on the sub-second latency criterion parameters. • Because of the interruption, you can never have an alert for a port such that the alert spans periods of time with different sub-second latency criteria on that port. Excluding a port from bottleneck detection When you exclude a port from bottleneck detection, no data is collected from the port and no alerts are generated for the port. All statistics history for the port is discarded. Alerting parameters for the port are preserved, so if you later include the port for bottleneck detection, the alerting parameters are restored. Per-port exclusions might be needed if, for example, a long-distance port is known to be a bottleneck because of credit insufficiency. In general, however, per-port exclusions are not recommended. Fabric OS Administrator's Guide 389 53-1002745-02