Fabric OS Administrator’s Guide 521
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CS_CTL-based frame prioritization
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CS_CTL-based frame prioritization
CS_CTL-based frame prioritization allows you to prioritize the frames between a host and 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 or hosts) 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.
Check with your host and storage manufacturer 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 to more fabric resources than are medium-priority frames, which
in turn are assigned to more fabric resources than are low-priority frames. The resources are
allocated according to the CS_CTL value, as shown in Table 77. The values are enabled by default
to ensure backward compatibility.
Alternatively, the user can apply CS_CTL auto mode. The CS_CTL auto mode uses only three
CS_CTL values, as illustrated in Table 78.
The values in the tables above represent chassis-level configurations. For configuration details, see
“Using CS_CTL auto mode at the chassis level” on page 522, and “Considerations for using
CS_CTL-based frame prioritization” on page 523.
Supported configurations
for CS_CTL-based frame prioritization
• CS_CTL-based frame prioritization is supported on all 8-Gbps and 16-Gbps platforms.
• All switches in the fabric should be running Fabric OS v6.0.0 or later.
TABLE 77 Fabric resources assigned to QoS priority for frame prioritization in CS_CTL default mode
CS_CTL value Priority
1–8 Low
9–16 Medium
17–24 High
TABLE 78 VCs assigned to QoS priority for frame prioritization in CS_CTL auto mode
CS_CTL value Priority
1Low
2Medium
3High
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