Dell EMC Unity: CIFS intermittently does not allow new sessions. (DellEMC Correctable)

Intermittently CIFS access runs into problems. Existing sessions work fine, but any new sessions to the array fail to connect. It resolves itself after a time period with no intervention from support. When looking into the SMBClient connectivity logs on the host the following event can be found:

If a packet trace is run during the problem you will see that the client successfully establishes a session through a SessionSetup call. Then attempts to do a TreeConnect call to the requested path. At that point the nas server will respond with a failure message and an NT status of STATUS_USER_SESSION_DELETED.

This is an issue caused by a code bug in 4.0 and 4.1. The issue arises when the session ID issued by the nas server is higher than 64,000. This is NOT the actual amount of active sessions, but just an ID value for the session. This problem can occur even if there are only a few thousand active sessions at any given point and will resolve itself once we start issuing sessions with lower session ID numbers again. 

Workaround:
At the current time there is a workaround that involves setting a parameter on the unity system. The parameter change lowers the current maximum amount of sessions from 127,000 to 64,000. This prevents the nas server from issuing a session id higher than 64,000, but also limits the maximum sessions to 64,000. The parameter change requires a reboot on the SP's. Please contact support and reference this knowledge base article to have the workaround applied. Once the code is upgraded, the parameter will need to be set back to the default value to allow for more than 64k sessions.

Permanent fix:
This issue will be fixed in the 4.2.x code release.

Dell Unity 300, Dell EMC Unity 300F, Dell EMC Unity 350F, Dell EMC Unity 400, Dell EMC Unity 400F, Dell EMC Unity 450F, Dell EMC Unity 500, Dell EMC Unity 500F, Dell EMC Unity 550F, Dell EMC Unity 600, Dell EMC Unity 600F, Dell EMC Unity 650F , Dell EMC Unity Family |Dell EMC Unity All Flash, Dell EMC Unity Family, Dell EMC Unity Hybrid ... View More View Less