Buffer to buffer credits alerts

[Gary.Williams]

We have just upgraded the MDS 9509 switches from 4.2.5 > 5.0.4d. Since the upgrade we have been getting the below alerts about every 10 minutes on different ports but on both switches that were upgraded

Event Description:RMON_ALERT WARNING(4) Falling:iso.3.6.1.4.1.9.9.289.1.2.1.1.38.17305600=0 <= 0:65500, 4 Severity Level:2

and

Event Description:RMON_ALERT WARNING(4) Rising:iso.3.6.1.4.1.9.9.289.1.2.1.1.38.17305600=10 >= 10:65500, 4 Severity Level:2

I understand that the issue is to do with "fcIfTxWtAvgBBCreditTransitionToZero" thresholds but I am not sure if this is something to be concerned about?

My understanding is that the buffer credits are being drained, the ports in question are not ISL ports but storage ports and replication applicance ports

[dakester · Accepted solution]

Hi,

There is a new feature that is automatically enabled at 5.0(4) and 4.2(7a).
http://www.cisco.com/en/US/docs/switches/datacenter/mds9000/sw/5_0/release/notes/nxos/mds_nxos_rel_notes_504.html#wp709740
Slow Drain Device Detection and Congestion Avoidance

Configuring Slow Drain Device Detection and Congestion Avoidance (4.2)
http://www.cisco.com/en/US/docs/switches/datacenter/mds9000/sw/nx-os/configuration/guides/int/int_cli_4_2_published/intf.html#wp1703520

Configuring Slow Drain Device Detection and Congestion Avoidance (5.0)
http://www.cisco.com/en/US/docs/switches/datacenter/mds9000/sw/5_0/configuration/guides/int/nxos/intf.html#wp1743661

The RMON email alerts you are getting correspond to the output of

show system internal snmp credit-not-available
Module: 1      Number of events logged: 36
-------------------------------------------------------------------------------------------------------------
Port     Threshold Rising/Falling  Interval(s)  Event Time              Type      Duration of time not available 
-------------------------------------------------------------------------------------------------------------
Fcx/y    10/0(%)                   1            Sat Feb 26 17:21:24 2011 Rising    10%           

This reads that the fc interface waited 100ms (10% of 1 Second) before receiving an R_RDY (credit) to send.

Consider contacting the vendor(s) of the devices attached to the interfaces generating these alarms.
Tell the Vendor(s) that withholding R_RDY over 100ms is a symtom of a problem.

credit-not-available within 100ms is not a big issue, unless a many credits are not availalbe for longer durations, such as 500ms.

To see if it is causing frame drops, use the following command,
show logging onboard timeout-drops
This command will display the total timeout discards per interface and the timestamp in the latest specified duration.
A timeout discard is a frame that was dropped because it was in the fabric for over 500ms, usually because an end device did not grant permission (R_RDY) for the switch to send to it.

You can see the defaults for port monitor with this command:

switch#show port-monitor

Reference for show port monitor
http://www.cisco.com/en/US/docs/switches/datacenter/mds9000/sw/nx-os/command/reference/CR04_sh_ps5989_TSD_Products_Command_Reference_Chapter.html#wp312577

Regards,

David

[T lA]

show logging onboard flow-control timeout-drops

This is the correct command to show drops