Western Digital Came out with the WD Black2 Dual Drive late 2013. It is a 120GB SSD mounted on top of a 1TB 5400 RPM HDD that fits in a standard 2.5" 9.5mm drive bay. It was being offered as an option for dual drive configurations in laptops with a single drive bay. It didn't get much attention as it was quite expensive, just as much as a separate 120GB SSD and 1TB drive. At launch it also did not have OS X support. Since it shares the SATA bus you need a configuration utility for the OS to see both drives. Now over a year later two things have happened. First they now have Mac support, second the price has dropped. I was able to get mine from Amazon for $130. The package includes a USB 3.0 to SATA cable and a link to downloading the firmware update and the drive configuration utility. You have the option of setting it up as a Core Storage Device (fusion drive) or as separate drives. I popped it into my 17" MBP and ran the firmware update utility (required for Macs) then set it up as a Fusion Drive. I then used disk utility to copy over the OS from my 750GB Momentus XT (I used thunderbolt instead of the included USB 3.0). It was a bit slow at first boot because of indexing. It also behaves like the Momentus XT where the first run of an application is slow as it learns what goes onto the SSD. It is noticeably faster than my previous setup with the Momentus XT. Writes are capped at 140MB/s while reads are around 380MB/s in my testing. So far I haven't experienced any slow down or stutters although one time waking from sleep took longer than usual. Battery life seems about the same but then again my 17" is used as a desktop. I just wanted to post this for those with older MBPs that are looking for a good compromise of speed and capacity and still want to keep the optical drive. Note that for a little bit more you can get a 500GB SSD which may suit your needs better, also software managed dual drives can have their own reliability issues so do your research.
