Руководство По Проектированию для Cisco Cisco Nexus 5010 Switch
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Four user-defined traffic classes: Of these, two can be no drop (for a total of three no-drop classes in
addition to the FCoE class).
All policy maps, including the one configured by the user, have class-fcoe.
You can verify the traffic class allocation by using this command:
show policy-map [system]
Buffering and Queue Limits on Cisco Nexus 5500 Platform
Buffering depends on the hardware platform, and it is different on the Cisco Nexus 5010 and 5020 than on the
Cisco Nexus 5500 platform. Buffering is performed at the ingress port, with a total of 480 KB per port. An egress
buffer also exists, with a size of 160 KB.
Table 3 lists the default buffer allocations per port on the Cisco Nexus 5500 platform.
Table 3.
Default Buffer Allocations per Port on Cisco Nexus 5500 Platform
Traffic Class
Ingress Buffer (KB)
class-fcoe
79.360
User-defined no-drop class with MTU < 2240
79.360
User-defined no-drop class with MTU > 2240
90.204
Tail-drop traffic class
22.720
class-default
478 minus the buffer used by other QoS groups
The table shows that if you do not create any traffic class in addition to the predefined class-default class, class-
default can buffer up to 478 KB of traffic. When you create an additional traffic class, the default buffer allocation
varies depending on the type of class. For instance, if you create a regular tail-drop traffic class, the default
allocation is 22.7 KB, unless you specify a larger size with the command queue-limit. If you do so, the buffer
space available to the class-default will be less.
If you want to increase the buffer space available to a user-created QoS group, you can do so from a network QoS
policy map by using the command queue-limit.
Note: Every new class requires an additional 18.880 KB, so the exact amount of buffer space that is left in
class-default equals 478 - Buffer space used by other QoS groups - 18.880 KB x Number of QoS groups.
class-default equals 478 - Buffer space used by other QoS groups - 18.880 KB x Number of QoS groups.
Buffering and Queue Limits on Cisco Nexus 5020 and 5010
On Cisco Nexus 5000 Series Switches other than the Cisco Nexus 5500 platform, each port has 480 KB of buffer
space: 320 KB for ingress and 160 KB for egress. By default, class-default gets approximately 243 KB, and QoS
group 1 for FCoE gets 76.8 KB. Table 4 lists the default buffer allocations.
Table 4.
Default Buffer Allocations per Port on Cisco Nexus 5020 and 5010
Traffic Class
Ingress Buffer (KB)
class-fcoe
76.8
User-defined no-drop class with MTU < 2240
76.8
User-defined no-drop class with MTU > 2240
81.9
Tail-drop traffic class
20.4
class-default
243.2 minus the buffer used by other QoS groups