I have had problems with hard drives weraring out. I have a few hundred Gb of data, about half are my photos. I have tried storing them on a local HD, a file server, and a nas device. When the photos were on a separate drive, that was the only drive that seem affected. I started using Windows Live Photo Gallery and that seemed to be the source of the problem. From when I first started using it, it seemed whatever drive had the photos on it was always working very hard and access performance was terrible. I unstalled Live Photo Gallery; activity went back down to normal. I tried using Google's Picasa and saw the same thing. It was making it impossible to manage my photo collection, and I was replacing hard drives every few months.
I recently uploaded all of my pics to a cloud storage service (that finally got folder syncing) and Live Photo Gallery and Picasa both work quite well now.