Buffer credit issues – Dell POWEREDGE M1000E User Manual
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Fabric OS Troubleshooting and Diagnostics Guide
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Buffer credit issues
8
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Port trunking is disabled.
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The port is not an E_Port.
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The port is not 2 Gbps, 4 Gbps, or 8 Gbps.
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The port connects to a switch other than the one you want it to.
To correct this issue, connect additional ISLs to the switch with which you want to
communicate.
•
The ports are not the same speed or they are not set to an invalid speed.
Manually set port speeds to a speed supported on both sides of the trunk.
•
The ports are not set to the same long distance mode.
Set the long distance mode to the same setting on all ports on both sides of the trunk.
•
Local or remote ports are not in the same port group.
Move all ISLs to the same port group. The port groups begin at port 0 and are in groups of 4 or
8, depending on the switch model. Until this is done, the ISLs will not trunk.
•
The difference in the cable length among trunked links is greater than the allowed difference.
Buffer credit issues
This section describes a trunk going on- and offline or hosts not being able to talk to a storage
device.
Symptom
Trunk goes offline and online (bounces).
Probable cause and recommended action
A port disabled at one end because of buffer underallocation causes all the disabled ports at the
other end to become enabled. Some of these enabled ports become disabled because of a lack of
buffers, which in turn triggers ports to be enabled once again at the other end.
While the system is stabilizing the buffer allocation, it warns that ports are disabled because of a
lack of buffers, but it does not send a message to the console when buffers are enabled. The
system requires a few passes to stabilize the buffer allocation. Ultimately, the number of ports for
which buffers are available come up and stabilize. You should wait for stabilization, and then
proceed with correcting the buffer allocation situation.
Getting out of buffer-limited mode
Occurs on LD_Ports.
1. Change the LD port speed to a lower speed (of non-buffer limited ports).
2. Change the LD port’s estimated distance to a shorter distance (of non-buffer limited ports).
3. Change LD back to L0 (of non-buffer limited ports).
4. If you are in buffer-limited mode on the LD port, then increase the estimated distance.
5. Enable any of these changes on the buffer-limited port or switch by issuing the commands
portDisable and portEnable.