MS Server 2008 Standard x64 running Symantec BE 12 SP3. Backup up to a Dell 124T LTO3-60 tape library connect via Adaptec 29160-160U SCSI card. One day backups are running at 900MB per minute to 1300MBPM. Next day they top out at 181MBPM. Drivers for 29160, Tape Library, and symantec's drive for tape drive have not changed. Tested with Dell for 5 hours, including using a dos utility that writes bypassing the backup software, still showed extreamly slow through put. They swapped out the tape drive, still same problem. Desperate for an answer to this problem.