I experienced this when I upgraded from vSphere 5.0 update 2 host to vSphere 5.1 update 1 I noticed an issue with the Isassd daemon, after the update manager finished with the upgrade the Isassd starts to write a lot of messages. For just 5 minutes the syslog server received 170k log messages from the upgraded host alone.
This message kept popping up in the logs:
esxihost.domain.loc lsassd: 0x6eb11b90:Terminating on fatal IPC exception
To solve this problem you first have to leave the windows domain. Select the host-Configuration – Authentication Services – properties. When you click to leave domain, the many logging hast stopped immediately.