Stefan Mileschin

Most modern SSDs come with some form of hardware encryption. On these drives with hardware encryption, it’s usually permanently turned on - all data written to the NAND is typically stored in encrypted form. This stems from the fact that all writes to NAND had to be scrambled to begin with (writing long repeated strings of data to NAND can cause problems for data retention). The earliest implementations weren’t sophisticated enough to be considered real encryption, but these days it’s not uncommon to see hardware AES-128/256 support.

The bad news has been that relying on OS driven filesystem encryption always meant the use of software encryption on top of your drive’s native encryption. This was particularly a problem on SandForce based drives, where full disk encryption basically ruined any of the performance advantages of the controller’s native compression/de-dupe (you can’t further reduce encrypted data). Other drives suffered (just not as much) due to the added overhead from having to leverage the host CPU to encrypt all data before writing it to disk. There’s also the fact that if you encrypt your entire drive (free space included), the drive ends up looking like a completely full drive - which has performance implications of its own. This was the world that existed with BitLocker under Windows 7 and FileVault under OS X.

http://www.anandtech.com/show/6891/h...h-crucial-m500