So that would be a large cupboard full then.
Then came tape drives - enough to try the patience of a saint.
I'm probably miles out but i reckon 2 and a half million floppies should do the job nicely. Assuming each disc takes 30 seconds then you'd be fully backed up in only 2 and a half years. Oh and if a box of 10 discs costs £3 the whole job would cost a mere £750,000