Look here for information about SNSDATA symbolic FRU.

This is a portion of the SCSI sense data associated with the unit reference code (URC); it is not a failing item in and of itself. This data is referenced by certain failure isolation procedures within the All 3995 Publications and Documentation at http://snjlnt02.sanjose.ibm.com/tape/tapetec.nsf/pages/3995pub or the 3996 Maintenance Information shipped with the 3996 Optical Library.