Configuring The Congestion Drop Timeout Value For Fibre Channel; Configuring The No-Credit Frame Timeout Value For Fibre Channel - Cisco MDS 9000 Series Configuration Manual

Congestion Detection, Avoidance, and Isolation
(Optional) Depending on the Cisco MDS NX-OS release version that you are using, use one of the following commands
to disable the FCoE pause drop timeout for edge or core ports:
• Cisco MDS NX-OS Release 8.1(1) and earlier releases
switch(config)# no system default interface pause mode {core | edge}
• Cisco MDS NX-OS Release 8.2(1) and later releases
switch(config)# no system timeout fcoe pause-drop default mode {core | edge}

Configuring the Congestion Drop Timeout Value for Fibre Channel

When a Fibre Channel frame takes longer than the congestion timeout period to be transmitted by the egress
port, the frame is dropped. This option of the frames being dropped is useful for controlling the effect of slow
egress ports that lack transmit credits almost continuously; long enough to cause congestion, but not long
enough to trigger the no-credit timeout drop. These drops are counted as egress discards on the egress port,
and release buffers into the upstream ingress ports of the switch, allowing unrelated flows to continue moving
through them.
By default, the congestion timeout value is 500 ms for all port types. We recommend that you retain the default
timeout for core ports and configure a lower value (not less than 200 ms) for edge ports. The congestion
timeout value should be equal to or greater than the no-credit frame timeout value for that port type.
To configure the congestion frame timeout value for the Fibre Channel, perform these steps:
Step 1
Enter configuration mode:
switch# configure terminal
Step 2 Configure the Fibre Channel congestion drop timeout value, in milliseconds, for the specified port type:
switch(config)# system timeout congestion-drop milliseconds logical-type {core | edge}
The range is 200-500 ms in multiples of 10.
Step 3
(Optional) Revert to the default value for the congestion timeout for the specified port type:
switch(config)# no system timeout congestion-drop default logical-type {core | edge}

Configuring the No-Credit Frame Timeout Value for Fibre Channel

When a Fibre Channel egress port has no transmit credits continuously for the no-credit timeout period, all
the frames that are already queued to that port are dropped immediately. As long as the port remains in this
condition, newly arriving frames destined for that port are dropped immediately. These drops are counted as
egress discards on the egress port, and release buffers in the upstream ingress ports of the switch, allowing
unrelated flows to continue moving through them.
No-credit dropping can be enabled or disabled. By default, frame dropping is disabled and the frame timeout
value is 500 ms for all port types. We recommend that you retain the default frame timeout for core ports and
configure a lower value (300 ms) for edge ports. If the slow-drain events continue to affect unrelated traffic
flows, the frame timeout value for the edge ports can be lowered to drop the previous slow-drain frames. This
Configuring the Congestion Drop Timeout Value for Fibre Channel
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