Hi all, I've got a mid 2012 13" Macbook Pro. I've bought a Samsung 850 Evo 500gb from Amazon for it and am having a horrible time trying to get the thing to work. Initially I just installed the SSD in the HDD bay as you'd expect and attempted a clean install of Yosemite from USB. The install was excruciatingly slow - taking 3 hours to move from 13 minutes to 12 minutes with very little activity in the install log and very very rare signs of activity on the USB stick activity LED. I booted the original drive (10.10.2) via USB adapter and attempted to move files to and from the (freshly reformatted) SSD, I found that whilst the transferring of data itself was fast, it would pause and hang for moments whilst doing so, meaning a 200mb video file took close to 5 minutes in total to copy. Playback of the file from the SSD exhibited this same stop-start access. I next attempted to connect the SSD by the USB adapter. Yosemite installed quickly, booted and ran lightening fast. I put the SSD back into the internal bay and everything slowed right down; booting took an age then clicking anything when it'd booted caused it to beachball/hang. I have tried enabling TRIM, this has had no effect. I've seen similar cases all over the internet but nothing definitive towards actually fixing, a lot of dead ends. One other forum user mentioned a read/write error in a log referring to the drive as (Null). I noticed this briefly when attempting to install Yosemite, the installer said that I was unable to install to (Null) for a split second on the drive selection screen - this accompanied with a 30 second or so delay for Disk Utility to load (and really slow format time) says that my Macbook really isn't getting along with the drive. I did think that the SATA cable could have somehow damaged itself in the process (as it's common knowledge that they are more fragile than the Natural History Museum's collection of Victorian Butterfly pressings) BUT the original drive, back in the Macbook performs normally - definitely no weird hangs or delays in accessing or writing data. The SATA cable was replaced by Apple less than 6 months ago as well and has been absolutely fine since then. This whole thing is really frustrating. There are no firmware updates available for the SSD and as far as I can see, no firmware/EFI updates for the Macbook. I'm leaning more towards this being a problem with the Macbook as the SSD performs flawlessly with the USB SATA adapter. My next step could be testing it in my old blackbook although I don't have any installation media for that to hand. Any ideas anyone... please?! EDIT - I have also cleared NVRAM and verified the SSD (with no errors) in disk utility.