Dual Drive Upgrade - The Good, Bad, and Ugly
The AppleCare on my mid-2012 15" MacBook Pro just expired, so I decided that was a good time to crack it open and see if I could extend its life by replacing the HDD with an SSD (500GB Samsung EVO 850). The Dual Drive kit would give me the bonus of using the original HDD for extra storage.
The repair was a breeze - up until the dreaded Step 8: removing the Bluetooth housing. I read all the comments about how everyone stripped those screws, so I was extra careful. The first screw came out with no problem. The 2nd screw - the 3.5mm one - not so much. I had to use a 1/16" drill bit to pop the head off the screw. After that, it was smooth sailing... except the original HDD won't mount on the desktop in my optical drive bay. Lots of poking around on the internet suggests that it might be because it's a SATA III drive, and those aren't happy in the optical bay of these particular machines - I'm still not really sure why it won't work.
The good news is, the speed boost that is gained from booting from an SSD cannot be understated. I had always heard how much faster SSD drives were, but I didn't expect the difference to be so dramatic. Highly recommend the SSD swap, but maybe simply getting an external enclosure for the HDD would be the way to go. Or, use a second SSD in the optical bay. Also, I had no idea about Trim and SSD drive performance. If you're considering making this upgrade, read about that. Luckily, OS X El Capitan will change Apple's Trim support for 3rd party drives, from what I understand.