Alright, I know that this is a very simplistic question, but I'm not sure where else to ask this, and it appears to me via the FAQ, that this is the correct place to ask questions about backup on systems. And since I'm more or less the accidental system administrator, then I'm going to ask.
We have an older Windows AD environment (Windows 2003 R2 Server). We've got a 400 GB Quantum tape drive that we have been using for years to do our backups. We just use Windows Backup and Restore utility for doing our backups. This has worked fine for years. Whenever we have to restore something from off of tape (a very rare occurance) that has worked fine as well. The backup script we use was one deveoloped by the last system admin we had, who left us about 4 years ago (we've never replaced him). I just follow his instructions and that's that.
I've noticed that the backups take about 300 GB on the tapes, so we're doing fine there, with lots of room for additional files. It is that which has me concerned. At our IT meeting today, it was brought up that we should add image files to the backups. (These files are very important documents, which are scanned in.) At this point I don't think that those images are being backed up. I can modify the former sys admin's script to include the relevant files/folders on the server. The server they're being stored on has a huge HD, something like 1 TB in size. Certainly more than enough to overwhelm one of the tapes for that Quantum tape drive. We're probably OK at the moment and will be for a while, but I'm not so sure about the future. If during a backup the tape fills up, will the Windows Backup and Restore utility prompt us to let us know that it needs a new tape? I assume the answer is yes, but I want to double check.
http://support.microsoft.com/default.aspx?scid=kb;en-us;816449 suggests that, if the backup is invoked via the UI, it will prompt for media like you would expect but, if it is invoked via the command-line (as a batch file or scheduled task would do), it will not.
Of course, that KB is for WinXP and you specify Win2003 but, in my experience, if it applied to XP, it applied to 2003.
You should look at alternative backup solutions; you are pushing enough data around now to warrant something a little more reliable than NTBackup. See if you can use the new requirement to get some budget for some dedicated software (e.g. Backup Exec, Arcserve) and maybe even an entry-grade auto-loader (e.g. an HP MSL 1/8) -- you probably don't want to have to worry about changing tapes mid-backup (especially if they run overnight).
Alternatively, perhaps spend that budget on a fast I/O card with an external port (e.g. USB3 or Firewire -- I would say eSATA, but I don't think you can hot-swap these) for your server and a handful of matching 2TB disks external disks, and going for a disk-based solution. You could probably continue to leverage NTBackup to these disks (as well as other specific backup tools) and may even have enough space to be able to keep more than one backup at a time on them.