This an old article from Linux Magazine, free to download, I found it to be an excellent and detailed review of the most common tools that exist to encrypt data in Unix systems, these different tools and methods are still valid and in use nowadays.
It provides some insights on encryption techniques, code quality, and the relative merits of the various solutions. The following encrypted file systems are examined:
In addition to looking at technologies and techniques the performance parameters for these encryption options are also assessed.
Download link(pdf article):