In one of my computers I had a 3 terabyte drive that I was using for storage of important files and it failed. Most of the files were backed up, but not all. The drive started giving random I/O errors so I stopped using it on a regular basis. Then I started getting smart errors and decided it was time to get the rest of my data off of it. That's when it decided to really give me a problem! It took 3 days to get stuff off of it and the reported capacity is now only 747 gigabytes.
I'm going to RMA the drive and hope the replacement lasts longer!