How strong of a magnet do you need to erase the data on an old-fashioned tape backup system (as in, one of those things that spins around with reels and tapes)?

According some articles, most of disk/tape will be unusable after

I found this inside an old server, it is a magnetic tape reader

Can damaged data be retrieved from Linear Tape-Open (LTO) backup

Innovation — we've got it taped!. Why the old ones are sometimes

Custom made reel to reel cassettes, any good?

How can magnets be used to separate junk in a junk yard? - Quora

How strong of a magnet do you need to erase the data on an old

Why did computer tape reels go back and forth instead of all the

Magnetic tape

Who invented magnetic tape recording? - Quora