Before you dismiss this as silly, let me explain :)
The only purpose of this encryption is to make the data inaccessible if the drive breaks down and I want to send it off for warranty replacement. This system needs to be able to boot without my supervision when I'm away - which precludes the use of any passwords. Right now I'm stuck with a drive that I can't warranty-replace, because it's too broken for me to wipe it.
Ideally the encryption would be based on a keyfile stored on the (unencrypted) system drive.
Options I've considered:
- TrueCrypt: requires the system disk to be encrypted too before it will agree to auto-mount (which requires the use of a password).
- BitLocker: unsupervised decryption impossible without a TPM module. Maybe it's possible with one? But my motherboards don't have TPM anyway.
- EFS: almost suitable, but cannot enable for the whole drive and copied files remain encrypted even when copied to a folder with no "encrypt" flag, both of which will be problematic in practice.