This OID names the FSM state that a MountInst object — the live, running instance of an NFS mount that was created from a MountDef and is (or was) actually attached — was in immediately before its current state. An admin compares this previous-state value against the current status to see the direction the MountInst object's workflow is moving, which matters for telling forward progress apart from a rollback. For example, if fsmPrev shows a later step than the current state, that indicates the MountInst workflow backed up to retry an earlier stage rather than advancing normally.