Cisco DS-C9216I-K9 Switch Guide - Page 365

Chapter 27 Configuring Traffic Management Control Traffic All switches support the following types of traffic: • Control Traffic • DataTraffic Control Traffic The Cisco MDS 9000 Family supports QoS for internally and externally generated control traffic. Within a switch, control traffic is sourced to the supervisor module and is treated as a high priority frame. A high priority status provides absolute priority over all other traffic and is assigned in the following cases: • Internally generated time-critical control traffic (mostly Class F frames). • Externally generated time-critical control traffic entering a switch in the Cisco MDS 9000 Family from a another vendor switch. High priority frames originating from other vendor switches are marked as high priority as they enter a switch in the Cisco MDS 9000 Family. Disabling Control Traffic By default, the QoS feature for certain critical control traffic is enabled. These critical control frames are assigned the highest (absolute) priority. We do not recommended disabling this feature as all critical control traffic will automatically be assigned the lowest priority once you issue this command. You can view the current state of the QoS configuration for critical control traffic using the show qos statistics command. Data Traffic Transaction processing, a low volume, latency sensitive application, requires quick access to requested information. Backup processing requires high bandwidth but is not sensitive to latency. In a network that does not support service differentiation, all traffic is treated identically; they experience similar latency and get similar bandwidths. The QoS feature in all switches in the Cisco MDS 9000 Family provides these guarantees from SAN-OS Release 1.3(x). Prior versions of the SAN-OS software only differentiated traffic priority based on control traffic. SAN-OS Release 1.3(x) enables you to take full advantage of the QoS capabilities. Data traffic can now be prioritized in four distinct levels of service differentiation: low, medium, high, or absolute priority. You can apply QoS to ensure that Fibre Channel data traffic for your latency-sensitive applications receive higher priority over throughput-intensive applications like data warehousing. OL-7753-01 Cisco MDS 9000 Fabric Manager Switch Configuration Guide 27-3