It is a technology that combines multiple storage devices into a single logical device and essentially allowing user to partition his space regardless of device storage borders.
This technology allows Fusion Drive devices support. And is required for FileVault encryption.
Most of new (year 2014) Mac computers are partitioned that way already and many computers updated to Mac OS X Yosemite get it with the update.
To check whether this technology enabled on your Mac or not, you can run the following command in Terminal:
diskutil cs list
In case you don’t have any of Core Storage configurations, Terminal will say “No Core Storage logical volume groups found”.
And if you have Core Storage, it will show you Core Storage table, like this one:
WARNING! Please check if you have Fusion Drive by checking your hardware or contacting your local Macintosh support service. Fusion Drive is a hardware configuration which is a combination of SSD and HDD in a single device which cannot be separated. If you have Fusion Drive than unfortunately you cannot disable Core Storage.
Also check that FileVault is disabled. In most cases disabling Fusion Drive disables Core Storage as well.
When you check for Core Storage configuration with Terminal command diskutil cs list, please find your Mac OS X system volume information and take a look at these lines:
If your Mac OS X partition is revertible, use this command to disable Core Storage:
diskutil cs revert [logical volume]
In this case this command will look like this:
diskutil cs revert 36B11150-B285-4C3C-876D-E70D4BABADC5
After running the revert process Terminal will ask you to reboot the system. After reboot you should have a Core Storage free Mac OS X. You can double check it with diskutil cs list command.
[NTFS for Mac OS X]
NTFS for Mac OS X doesn’t have any compatibility issues with Core Storage technology
[HFS+ for Windows]
If you are running HFS+ for Windows in a Bootcamp configuration, you won’t be able to see (or open) Mac OS X partition due to Core Storage restrictions. If you can disable Core Storage as described above, this will give you access to Mac OS X system drive from Bootcamp.