HP Brocade 8/12c Brocade Network Advisor SAN User Manual v11.1x (53-1002167-01 - Page 844

27 Bottleneck detection Bottleneck detection A bottleneck is a port in the fabric where frames cannot get through as fast as they should. In other words, a bottleneck is a port where the offered load is greater than the achieved egress throughput. Bottlenecks can cause undesirable degradation in throughput on various links. When a bottleneck occurs at one place, other points in the fabric can experience bottlenecks as the traffic backs up. The bottleneck detection feature detects two types of bottlenecks: • Latency bottleneck • Congestion bottleneck A latency bottleneck is a port where the offered load exceeds the rate at which the other end of the link can continuously accept traffic, but does not exceed the physical capacity of the link. This condition can be caused by a device attached to the fabric that is slow to process received frames and send back credit returns. A latency bottleneck due to such a device can spread through the fabric and can slow down unrelated flows that share links with the slow flow. A congestion bottleneck is a port that is unable to transmit frames at the offered rate because the offered rate is greater than the physical data rate of the line. For example, this condition can be caused by trying to transfer data at 8 Gbps over a 4 Gbps ISL. You can set alert thresholds for the severity and duration of the bottleneck. If a bottleneck is reported, you can then investigate and optimize the resource allocation for the fabric. Using the zone setup and Top Talkers, you can also determine which flows are destined to any affected F_Ports. You configure bottleneck detection on a per-fabric or per-switch basis, with per-port exclusions. NOTE Bottleneck detection is disabled by default. Best practice is to enable bottleneck detection on all switches in the fabric, and leave it on to continuously gather statistics. Supported configurations for bottleneck detection Note the following configuration rules for bottleneck detection: • The switch must be running Fabric OS 6.4.0 or later. • Bottleneck detection is supported on Fibre Channel ports and FCoE F_Ports. • Bottleneck detection is supported on the following port types: - E_Ports - EX_Ports - F_Ports - FL_Ports • F_Port and E_Port trunks are supported. • Long distance E_Ports are supported. • FCoE F_Ports are supported. 800 Brocade Network Advisor SAN User Manual 53-1002167-01