50 Terabytes is a rather significant amount of data. Are you sure you have that much? Unless you're archiving movies, it's actually difficult for most people to get beyond 5 to 10 TB, even if they are hoarders.

There a few different ways to look at this problem:

First, are you needing to access this data on a moment's notice all the time, or can your access wait to load the correct media?
Second, is most of what you're needing to access read-only?
Third, how much are you wanting to spend? 

The one thing I will say about tapes here: With the exception of 9-track tapes from the mainframe/minicomputer era, tape drives and tape formats seem to change every five years or so. Tape drive technologies have had a lot of dead ends. I used to have an 8mm data drive. Then I had a 4mm DAT drive. They're both defunct now, and if I wanted to get at that data now on my Macs or PC's, I'm going to have to get a SCSI card or interface and write drivers to support those drives. I've got data on DEC TK-50 tape cassettes - what a piece of crap those were. I've got data on 9-tracks at 1600 bpi and 6250 bpi - which I could still read on a mainframe if I wanted to pay to have it done. I'm now of the opinion that tape media, as an archival format, is a very fleeting thing - it isn't for the long term any more, simply because the technology moves on quickly enough to obsolete one tape drive and format after another.