System Backup: Pros and Cons of Tape

I am wondering what the pros and cons of certain backup methods are. In particular, what are the advantages and disadvantages of backing up to tape versus an external USB hard drive?

Currently, my company backs up around 15GB of data and system information nightly to 10/20 GB Travan tapes. We're on pace to surpass the capacity of these tapes in 6-8 weeks, and we're trying to determine if an extra $400.00 for new 20/40 GB tapes is worth the cost if we can get a USB hard drive for a about a quarter of that price that will hold the data we need to backup.

If we do decide to go with the external hard drive, should it be mirrored or set to backup like the tapes? If we back up to the hard disk, we'll need at least two drives (one to take home in case of a building disaster, and one to backup).

Or should we look to upgrade our Travan tape system to the newer DLT backup?

Any input will be greatly appreciated.

Thanks

I used tape at my old company. We used ArcServeIT with weekly differential and monthly cumulative backups. The good thing about tape is you can archive things when your hard drive fills up and store the tapes off site.

I visited a LARGE company a few years ago and they used tape and optical drives. They're big automated expensive systems that robotically change out the tapes, exercise the tapes and store them. They work in the terrabyte levels.

No matter your decision, you should have software to manage the backups for you. It makes it so much easier and if your System Admin goes on vacation, you can get someone to either load the tape for you or connect the external hard drive.