Is it just me, or has it been an awfully long time since HD's went up in size?

[M A V I C]

There's another issue as well. SATA drives are commonly specified with an unrecoverable read error rate (URE) of 10^14. Which means that once every 100,000,000,000,000 bits, the disk will very politely tell you that, so sorry, but I really, truly can’t read that sector back to you.

One hundred trillion bits is about 12 terabytes.

So pop 4 3TB drives into a Drobo, and you've got a 100% chance of that happening.