> Because it just looks like random data that hasn't been formatted. I'm guessing that SSDs also give up the secret if an attacker has access to custom firmwar

> Because it just looks like random data that hasn't been formatted. I'm guessing that SSDs also give up the secret if an attacker has access to custom firmware to read the wear-levelling metadata and finds a bunch of recent writes in the random data. At this point, unless speed or capacity are at a premium, it probably makes more sense to completely boot and run off of a fast USB drive. Linux + LUKS-header will be fairly obvious on the USB boot drive anyway, making plausible deniability pretty hard. What's the threat model? State-level attackers (e.g. journalists working with Snowden) or the border police wanting you to provide a passphrase for stored data or to boot a system? For the latter a good solution is don't transport anything important across the border.