VeraCrypt's approach to achieve plausible deniability for disk encryption:<p><a href="https://veracrypt.eu/en/Hidden%20Volume.html" rel="nofollow">https://veracrypt.eu/en/Hidden%20Volume.html</a>
This would be quite expensive to apply to whole-disk encryption, as you'd need 8x the size of the data that you want to store. Whether this is worth it or not depends on the threat model you're facing, of course.
This is a very poor advice at deniable encryption. The structure of the ciphertext is visible to the reader - when you get your decryption you know that it is one of many.<p>I presume the true deniable decryption would work in a way that fully hides the presence of the alternate contents. Note, however, that most encryption schemes are specifically designed to be non-deniable, so you'd be caught by simply using organically grown crypto before even decrypting anything.<p>For those interested in paranoia, I suggest looking into steganography and forward-secrecy schemes with transient secrets.