Certificate Based dataset encryption.
Certificate based would be the ideal way to go.
Then you have the option of:
- Adding a password to the Cert would be an option. For those that don't mind the need to enter a password before the partition is mounted.
- Have the Cert on any non encrypted partition to pass to GELI on boot. No user input required.
- Using a Certificate Authority Server (this seperates the certs from the server using them, so if seperated on the network, ie the NAS is stolen, unless the cert server is reachable, no decryption.
- Have the option of a tertiary Cert Authority incase the first is down.
Just my 2 cents.
This would give you the option to boot without user intervention as either having a cert on a partition of either a usb drive, or create a simple cert server available only available to your local subnet. Later would be preferred as say the File Server is stolen, unless they steal and put the cert server online, your stuff is still encrypted. You could even take this further by using trusts.
I believe GELI is capable of this. I could be way off though. Correct me if I'm wrong.