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Cisco Bug: CSCvs72258 - UCS 6332 - QoS change results in prolonged storage outage

Last Modified

Oct 17, 2020

Products (1)

  • Cisco Unified Computing System

Known Affected Releases

4.0(4c)A

Description (partial)

Symptom:
Directly following UCS System QoS configuration changes on 6332-16UP, one or more of the following is seen
 
•	Host OS or VIC Adapter logging shows extended storage connectivity issues (aborts etc.)
 
•	Upstream SAN switches may report UCS domain as exhibiting slow drain behaviour, as no RRDY’s are received from Fabric Interconnect and they send Link Reset (LR) to Fabric Interconnect
•	Following counter will not increment on an FC port which is up, showing no RRDY is being sent:
connect nxos a/b  
show hardware internal fc-mac 1 port x statistics | incl FCP_CNTR_MAC_CREDIT_IG_XG_MUX_SEND_RRDY_REQ  (where X is the port number)
show hardware internal fc-mac 1 port x link-event | E_LINK_LR will show Link Resets received from Upstream SAN switch, based on rate of traffic.
•	show interface fc1/X will show outbound LRR (Link Reset Response) incrementing, based on rate of traffic.
 
However, there is a unique signature for this issue which TAC can assist to verify

Conditions:
Issue is specific to UCS-FI-6332-16UP. 
Other Fabric Interconnect models are not affected

- Issue occurs after change of System QOS from default values when FC ports were up/enabled from most recent boot.
- Issue does not occur if System QOS has been changed from default values and Fabric Interconnect has been rebooted previously
 
Note: Default System QOS has only FC and Best Effort Ethernet enabled, with 50% weight each, with Normal MTU for Best Effort Ethernet.
Any System QOS configuration which differs from this is not a default configuration.
Most common trigger is to change Best Effort MTU to 9216 to allow Jumbo frames, however any System QOS change can trigger issue.
Immediately reverting the change does not recover the environment.
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