My son-in-law had 8 years of photos backed up on a Western Digital harddrive. Most we're of his 2 daughters as they grew up. To give you an idea of how many pictures we are talking about, they took 1700 when they we're on a 7 day Disney Cruise last year.
The harddrive crashed about 3 months ago. He had all backed up onto the external and deleted them from his desktop to make more room. The harddrive would show on the desk top but never showed any files. After trying several computers with the same results, he brought the external to me. I removed the hdd from the external case and mounted it into my desktop. It showed nothing.
He ended up taking it in locally and they could see nothing. They sent it to a company in California and after 2 months and $1400 he had 75% of his files back. They told him the problem was in the hardware used in the external, not the disc itself.
We learned a lesson from this. Those precious photos can be backed up on a external harddrive, but also need to be on another media. I have my photos on the desktop, an external drive, and will either put them to disc or mount a 2nd hdd in my computer. Which ever way I go, I'll have double redundancy...........
The sad thing is I've been reading this site for about 2 years. Those that make this site what it is have preached over and over about this same issue, and it took this experience to bring it home for me. I'm a slow learner, but I have learned............ Thank you for what you do.