Chapter 29. Disk Encryption Guide
Red Hat Enterprise Linux 5.3 now contains support during installation for file system encryption. This is not supported for earlier versions of Red Hat Enterprise Linux.
29.1. What is block device encryption?
Block device encryption protects the data on a block device by encrypting it. To access the device's decrypted contents, a user must provide a passphrase or key as authentication. This provides additional security beyond existing OS security mechanisms in that it protects the device's contents even if it has been physically removed from the system.