Upgrading to SSD on 2010 MBP I have a mid-2010 MacBook Pro, which I want to upgrade with an SSD in the Optical Drive slot and create a Fusion Drive (using the Terminal diskutil command in Recovery Mode) and then re-install OS X Yosemite on the newly created Fusion Drive. I have already upgraded the HDD from 250 GB to 1 TB and the RAM is 8 GB, upgraded from 4 GB. 

I need some advice because, while I know quite a lot about software (I study Computer Science at University), I'm not so good on the hardware side of things. So the questions I need answers for are:


What would be the best SSD to get for my Mac? I have been looking at the Samsung 840 Evo, but I was wondering whether something like the Samsung 850 Evo would be worth buying instead. Would I get the extra speeds it offers, seeming as my MacBook Pro can only support up to 3 GB/s instead of the 6 GB/s of newer models. Also the SATA connectors are only version 2, not 3.
When upgrading it, where do I put the SSD? Before the Fusion Drive came about, I've read that you should put the SSD in the slot where the HDD is, and put the HDD in the Optical Disk slot, as this will avoid problems with Sleep mode (because the SSD will be the boot volume). Is this still necessary with a Fusion Drive, because the system treats the 2 drives as one Logical Volume anyway?
Would I need to enable TRIM support with a Fusion Drive? Would the Samsung 840 Evo or anything else like that support all that I need?


Thanks for any help :)
re 1: hard to say - if you can spare the Money you should go for the 850 bc. of a (probably) better Garbage Collection (see #3), else go for the 840.

re 2: The best tutorial for replacing the optical drive with a harddrive (or SSD) can be found at iFixit.com, f.e. this one. You should search for the Tutorial for your model, the link i posted is probably not for your model.

re 3: There is a hot discussion going on if Trim should be enabled or not and if that is a bad thing. Fact is, Apple has Trim Support enabled only on its own OEM SSDs and disabled it for third party drive. There are Tools to enable TRIM Support, but it could be a not necessary bc. of a better Garbage Collection within the SSD Firmware (see this article and this Article). For general Infos i recommend this Article from Samsung 

BTW, to create a homemade Fusion Drive you need to use the 'Core Storage Volume' Command. You can look it up with 

man diskutil


look at the 'coreStorage' section. There are some tutorials for creating a homemade Fusion Drive, but it's a very painful process.