HP Cisco MDS 9222i Cisco MDS 9000 Family Fabric Manager Configuration Guide - - Page 1328

Chapter 64 Configuring Fabric Congestion Control and QoS QoS Send documentation comments to [email protected] About Service Policy Definition Service policies are specified using policy maps. Policy maps provide an ordered mapping of class maps to service levels. You can specify multiple class maps within a policy map, and map a class map to a high, medium, or low service level. The default priority is low. The policy map name is restricted to 63 alphanumeric characters. As an alternative, you can map a class map to a differentiated services code point (DSCP).The DSCP is an indicator of the service level for a specified frame. The DSCP value ranges from 0 to 63, and the default is 0. A DSCP value of 46 is disallowed. The order of the class maps within a policy map is important to determine the order in which the frame is compared to class maps. The first matching class map has the corresponding priority marked in the frame. Note Refer to http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a00800949f2.shtml for further information on implementing QoS DSCP values. Note Class maps are processed in the order in which they are configured in each policy map. About Service Policy Enforcement 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 is not enforced. You can only apply one policy map to a VSAN. Note You can apply the same policy to a range of VSANs. About the DWRR Traffic Scheduler Queue The Cisco NX-OS software supports four scheduling queues: • Strict priority queues are queues that are serviced in preference to other queues-it 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 high, medium, and low priority traffic queues. 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 the 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). Table 64-2 describes the QoS behavior for Generation 1, Generation 2, and Generation 3 switching modules. 64-8 Cisco MDS 9000 Family Fabric Manager Configuration Guide OL-17256-03, Cisco MDS NX-OS Release 4.x