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Ingress Port Rate Limiting
Applying a Service Policy
When you have configured a QoS data traffic policy, you must enforce the data traffic configuration by
applying that policy to the required VSAN(s). If you do not apply the policy to a VSAN, the data traffic
configuration will not be enforced. You can only apply one policy map to a VSAN.
You can apply the same policy to a range of VSANs.
Scheduling Traffic
The SAN-OS software supports four scheduling queues:
•
•
Use the qos dwrr-q command to associate a weight with a DWRR queue.
The DWRR scheduler services the queues in the ratio of the configured weights. Higher weights translate
to proportionally higher bandwidth and lower latency. The default weights are 50 for high queue, 30 for
the medium queue, and 20 for the low queue. Decreasing order of queue weights is mandated to ensure
the higher priority queues have a higher service level, though the ratio of the configured weights can vary
(for example, one can configure 70:30:5 or 60:50:10 but not 50:70:10).
Ingress Port Rate Limiting
A port rate limiting feature is available in SAN-OS 1.3(x). This feature helps control the bandwidth for
individual FC ports. Port rate limiting is also referred to as ingress rate limiting because it controls
ingress traffic into a FC port. The feature controls traffic flow by limiting the number of frames that are
transmitted out of the exit point on the MAC. Port rate limiting works on all Fibre Channel ports.
Port rate limiting can only be configured in switches in the Cisco MDS 9100 Series.
This command can only be configured if the following conditions hold true:
•
•
The rate limit ranges form 1 to 100% and the default is 100%.
Default Settings
Table 27-1
Cisco MDS 9000 Fabric Manager Switch Configuration Guide
27-6
Strict-priority queues are queues that are serviced in preference to other queues. A strict-priority
queue is always serviced if there is a frame queued in it, regardless of the state of the other queues.
QoS assigns all other traffic to the DWRR scheduling queues:
Use dwrr-q high option to schedule high priority traffic.
–
Use dwrr-q medium option to schedule medium priority traffic.
–
Use dwrr-q low option to schedule low priority traffic.
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The QoS feature is enabled using the qos enable command.
The command is issued in a Cisco MDS 9100 series switch.
lists the default settings for FCC, QoS, and rate limiting features:
Chapter 27
Configuring Traffic Management
OL-7753-01
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