Old hard drives - I have had them for 3 years - on my servers at home started to fail, so I had to replace one RAID-5 array. I bought 5 2TB drives and used software RAID-5 function in Windows Server 2008 R2 to create a monstrous 7.5TB (usable space) drive out of these 5 disks.
I only use soft RAID because the disks can be read by any Windows Server, whereas hardware RAID protects well against a drive failure, but if it is the controller that dies, you may be out of luck - who knows if this model would be even available a few years down the road, and most controllers use proprietary data formats, so the disk arrays are not portable between them.
Anyway, I built the array and starting formatting it. After the first 24 hours, the format was 13% complete. Next day (today) it is up to 26%.
Puzzle for the readers - how long do you think the format is going to take in total? Do not post the reasoning, just the number :-). I will post the final answer (and why) when the format completes.