Jim Gray of Microsoft Research talks about data storage
1. Right now, once your data sets get into the Terabyte range, it's cheaper to Fed-Ex a computer full of disks than it is to transfer the data over the internet.
2. Disk capacity increases faster than disk access speed, by a factor of 10. This means that when disk technology reaches its technical dead end in the Petabyte scale, your disk will be too big to access all of it's data in any practical time span, much less back up.
I have to think that some of the current basic-research pie in the sky stuff will come online before that time -- carbon nanotube random access storage with access times closer to current RAM access speeds.
I started adding it up the other day, and realized I had something like 1/3 a terabyte on line at my house -- 300 gigabytes or thereabouts spread over 5 computers. How the eff would I ever back that up economically? Right now I periodically burn off all my master music recordings and archives of some of my writing, and figure the rest is chaff.
Thing is, nearly everything about my life is chaff -- the only things I really care about -- my kids, my wife, aren't amenable to back up.