Since version 2.10 DbDefence supports AES Instruction Set on modern CPUs. This speeds up encryption process making it 5-8 times faster. However considering complete I/O of the server the difference is not that big. The benefit from that feature more noticeable on heavily loaded systems with large databases.

You can see if your CPU supports it by executing dbd_status

Advanced Encryption Standard (AES) Instruction Set is an extension to the x86 instruction set architecture for microprocessors from Intel and AMD proposed by Intel in March 2008. The purpose of the instruction set is to improve the speed of applications performing encryption and decryption using the Advanced Encryption Standard (AES).
--- Wikipedia.

List of supported CPUs from Wikipedia

Intel
- Intel Westmere based processors, specifically:
  - Intel Gulftown processors.
  - Intel Clarkdale processors (except Core i3).
  - Intel Arrandale processors (except Core i3, Core i5-4XXM).
- Intel Sandy Bridge processors:
  - Desktop: all except Core i3.^[3]
  - Mobile: all Core i7. Though the Intel web pages originally listed the 2630QM and 2635QM as not supporting it, those web pages have been updated to indicate that they do.^[4]^[5] Several vendors have shipped BIOS configurations with the extension disabled,^[6] requiring a BIOS update to fix..^[7]
- Intel Ivy Bridge processors
- Intel has a list of processors that support AES-NI on their web site^[8]
AMD
- AMD Bulldozer based processors.^[9]