I have a 2TB Samsung HD204UI SATA hard drive docked into a USB 3.0 Sharkoon Speedport Duo that I use to backup another external hard drive from time to time. I'm using it on a 15 inch Retina MacBook Pro and El Capitan 10.11.3. Here are the symptoms: Sometimes it will take longer than other disks to appear on the desktop when I mount it (often a minute or so) There is a "DamagedFiles" folder on it with two ".DSstore" files on it (probably some normally-hidden Finder files) Even if it does mount properly, sometimes it appears as if there was nothing on it (0 items) Sometimes applications complain about not being able to write to it However: Running First Aid in the new Disk Utility says everything's fine Most of the time, everything is fine even if it takes a bit longer to mount So, I'd guess these are symptoms of a failing hard drive (It's just a backup so if it does fail I don't lose anything important). But before I get a new one, I want to make sure this is really the issue and not something else. Could it possibly be the dock behaving strangely? Should I try reformatting it? Or should I just not take risks and steer clear of this drive and get a new one?