I am running BackupExec 12.5 on a Windows 2003 Standard server. It connects to various other 2003 and 2008 servers and does a full backup each weeknight.
One day last week, the software started recognizing the tapes as full well short of being full. The last successful backup had 313GB in the byte count. The backups are now stopping at 275GB or so and the software is asking for another tape.
My first inclination was to replace the tape drive. It's been giving signs that it was wearing out for a while (throwing random "data grade" errors on the tapes, locking up some nights, etc.). I ordered one online and NDA shipped it. Put it in over the weekend and re-tried the full backup. The first attempt made it to 300GB on the nose before it stopped. The software also reported a "voltage error" so I shut the server down and re-seated the power cable and SCSI cable and that error went away. When I re-tried the backup again, it stopped in exactly the same place as before (275GB or so).
The tape capacity is 200GB native / 400GB compressed. As noted, the last successful backup completed at 313GB. I've tried changing the compression option from "Software" to "Hardware (if available, otherwise software)" and it didn't help.