Many users around the net have been realizing after installing the OS X Yosemite beta the partitions on their hard drive were converted to Logical Volumes. I’m not entirely sure why Apple chose to do this, but it makes resizing and deleting partitions on the fly 10x harder! I haven’t found a good solution as of this writing, but make sure you are aware of this!
Apple introduced “Core Storage” with the release of OS X 10.7 Lion. All Fusion drives use Core Storage. A Fusion drive is pretty much just an SSD and traditional spinning hard drive combined into one logical drive. Normally these drives would show up separately, but with the help of Core Storage, they can be turned into one logical volume. It’s possible to create your own Fusion Drive with a separate SSD and HDD by using Core Storage. There are a few tutorials around the web that can help with this. I’ve created 3 of my own “Fusion Drives” using these guides.