The default approach for storing files on drives other than your boot drive is to get an external storage device and then copy your files to it; however, by doing so you leave open the possibility of someone getting your drive and accessing your data. To secure the files you place on such drives, there are several approaches you can take, including encrypting files or the drive itself, and using special setups to require two or even more physical drives be attached before you can access the data on them. Continue reading
Options for securing external storage in OS X
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When you set up an external drive for use with your Mac, you may wish to partition it for various uses. For instance, you might want to isolate automatic Time Machine backups from manual ones. The classic way to do this on a single drive is to use Disk Utility to partition it, where you split the drive into two or more logical volumes that the system sees as separate file systems. Since OS X supports Apple’s CoreStorage volume management technology, if you wish to do this then you can do so via classic partitioning, as well as through CoreStorage. 
In OS X 10.7 Lion, Apple switched its FileVault encryption technology from relying on disk images, to using a volume management technology called CoreStorage. This provides a layer between the OS and the physical partitions on a local drive, allowing not only full-disk encryption options, but also spanning of a single logical volume across multiple physical partitions. 
Data encryption is an important consideration if you keep sensitive or otherwise private documents on your Mac. While data encryption is not always necessary, such as for servers that can be physically secured in a closet, if a system can be stolen or opened so the drives can be removed, encryption is perhaps the only way to ensure your data is secure.