If you are a MacBook user that rarely uses the optical drive on your machine, but routinely runs out of storage space on your HDD inside the notebook, OWC has a new product for you. The device is called the OWC Data Doubler.
The Data Doubler is an optical to SATA HDD converter bracket kit that sells for $79.99. The bracket allows you to add up to an extra 640GB HDD or SSD to the inside of the MacBook. Any 9.5mm tall 2.5-inch SATA SSD or HDD will fit inside the bracket.
You apparently have to open your Mac up and remove the optical drive and install the bracket into the bay. You can then use the Apple disk Utility program to set up and partition the new drive. Once the bracket is installed, you can use the drive for Time Machine, a RAID array, or one large SPAN volume. There are several bracket models available to fit different MacBook models.