Symptoms

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 examining the SMBClient connectivity logs on the host, you can find the following event: If a packet trace is run during the problem, you 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 responds with a failure message and an NT status of STATUS_USER_SESSION_DELETED.

Cause

This is an issue caused by a code issue 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 number 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 resolve itself once we start issuing sessions with lower session ID numbers again.

Resolution

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 number 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. Contact support and reference this knowledge base article to have the workaround applied. Once the code is upgraded, the parameter must 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.

Support Cases