Brocade Network Advisor SAN User Manual v12.1.0 - Manual (Page 1039)

Brocade Network Advisor SAN User Manual 991
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Bottleneck detection
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Restarting a Top Talker monitor
Procedures in this section pertain to restarting monitors created on systems using the legacy Top
Talkers feature and not those created with Flow Vision.
For systems using Fabric OS version 7.2 or later, when you select a device or device port, and then
select Monitor > Performance > Top Talkers, a message displays that you can use Flow Vision to
provide Top Talkers monitoring. You have these options:
• To use Flow Vision, delete existing monitors, then use the Add Flow Definition dialog box to
define an initiator and target port pair for monitoring. Refer to
Chapter 30, “Flow Vision” for
more information.
• Clicking OK opens the legacy Top Talkers dialog box. To use the legacy Top Talkers feature, you
must deactivate existing flows defined for the switch for Flow Vision.
To restart a top talker monitor, perform the following steps:
1. Select the dialog box of the Top Talker monitor you want to restart.
Refer to steps 1-5 under “Configuring a fabric mode Top Talker monitor” on page 986 or
“Configuring an F_Port mode Top Talker monitor” on page 988 to display this dialog box.
2. Click Continue.
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.