Reference Guide

∙ QoS zones that use D,I notation should not be used for loop or NPIV ports.
∙ If QoS is enabled, an additional 16 buffer credits are allocated per port for 8-Gbps ports in Extended Mode (LE). Refer to
Managing Long-Distance Fabrics on page 483 for information about buffer credit allocation in extended fabrics.
∙ If some ports in a trunk group have QoS enabled and some ports have QoS disabled, then two different trunks are formed, one
with QoS enabled and one with QoS disabled.
∙ QoS mode cannot be explicitly enabled on simulation ports (SIM ports). CS_CTL mode can be enabled on SIM ports.
CS_CTL-based frame prioritization
CS_CTL-based frame prioritization allows you to prioritize the frames between a host and a target as having high, medium, or low
priority, depending on the value of the CS_CTL field in the FC frame header.
The CS_CTL field in the FC header can be used to assign a priority to a frame. This field can be populated by selected end devices
(storage and host) and then honored by the switch, which assigns the frame, based on the value in the CS_CTL field, to allocate
appropriate resources throughout the fabric. This method of establishing QoS is an alternative to the switch-controlled assignment that
uses zone-based QoS.
ATTENTION
Check with your host and storage manufacturers to determine whether they support Fibre Channel CS_CTL prioritization on
their devices.
High-, medium-, and low-priority frames are allocated to different sets of fabric resources. High-priority frames are assigned more fabric
resources than medium-priority frames, which in turn are assigned more fabric resources than low-priority frames. The resources are
allocated according to the CS_CTL value, as shown in Table 76. The values are enabled by default to ensure backward compatibility.
TABLE 76 Mapping of CS_CTL values to QoS priority for frame prioritization in CS_CTL default mode
CS_CTL value Priority
1-8 Low
9-16 Medium
17-24 High
Alternatively, the user can apply CS_CTL auto mode. The CS_CTL auto mode uses only three CS_CTL values, as illustrated in Table 77.
TABLE 77 Mapping of CS_CTL values to QoS priority for frame prioritization in CS_CTL auto mode
CS_CTL value Priority
1 Low
2 Medium
3 High
NOTE
The values in the tables represent chassis-level configurations. For configuration details, refer to Using CS_CTL auto mode at
the chassis level on page 399, and Considerations for using CS_CTL-based frame prioritization on page 400.
Supported configurations for CS_CTL-based frame prioritization
CS_CTL-based frame prioritization is supported on all 8-, 16-, and 32-Gbps platforms.
All switches in the fabric should be running Fabric OS v6.3.0 or later.
Optimizing Fabric Behavior
Brocade Fabric OS Administration Guide, 8.0.1
398 53-1004111-02