I'm wondering if anyone else is having issues with 2TB 850 Pro SSDs in Mid 2012 MacBook Pros. I have a Mid 2012 MacBook Pro (15-inch 2.3Ghz Intel Corei7, 8GB Memory, OS X Yosemite 10.10.5) For over a year now I've been running it what a 512G Samsung 840 Pro boot disk and a 1TB 840 EVO in the CD bay (using an adapter tray). I want to change out the 1TB EVO for a 2TB PRO but each time I image the 1TB to the 2TB my machine starts acting weird. Writes don't happen, the system hangs or just generally works poorly. I put the 1TB back in and the system picked right up and worked without issues. A friend suggested it could be a permissions issue or something, so I imaged it again. Same results. I then used TechTool Pro 8 to make the image. Also same results. Here's the part that is just blowing my mind... If I take the non-working 2TB disk having just imaged it and attach it using a SATA-USB adapter, it works fine. The system runs well and the performance is pretty good. Obviously I can't run around with my second drive hanging six inches off my USB port. The only idea I have is that there is some sort of firmware issue with running a >1TB on the internal SATA port meant for the CD drive, but honestly, I don't know why it wouldn't work. Is anyone aware of any issues like this or have suggestions on what to try?