External hard drive not working on yosemite

Somehow, everything is magically working fine now.

I actually called Apple support and began a remote session with technical support. Of course, as soon as the guy is able to view my screen I have no problem mounting the external drive and viewing the files. So, I guess the answer in this instance is to call Apple support and then your external drive will magically appear in Yosemite.

For my hard drive that doesn't show up at all, the problem is not Yosemite per se. It's the USB3 driver incompatibility. Try using a USB2 cable (micro USB just like an android charger cable that plugs in half of the slot on your hard drive) and it will work. Or try connecting it to an older computer that has USB2 ports on it (with the original USB3 cable) and it will work BOTH on Yosemite and Mavericks. Of course it will transfer data at USB2 speeds. Apple screwed up the drivers again so we have to wait for them to 1. receive thousands of complaints 2. wait for eternity to acknowledge there's an issue. 3. take their sweet time fixing the USB3 drivers. Until then you can get by with USB2 cables. I hope this helps!

For my hard drive that doesn't show up at all, the problem is not Yosemite per se. It's the USB3 driver incompatibility. Try using a USB2 cable (micro USB just like an android charger cable that plugs in half of the slot on your hard drive) and it will work. Or try connecting it to an older computer that has USB2 ports on it (with the original USB3 cable) and it will work BOTH on Yosemite and Mavericks. Of course it will transfer data at USB2 speeds. Apple screwed up the drivers again so we have to wait for them to 1. receive thousands of complaints 2. wait for eternity to acknowledge there's an issue. 3. take their sweet time fixing the USB3 drivers. Until then you can get by with USB2 cables. I hope this helps!