[ale] Filesystem encryption

[jimbutler1234567890 at gmail.com (Jim Butler)]

  Hi Linux People!
I have a question and am looking for some experienced suggestions.
I saw a server recently that had filesystem encryption applied to the 
entire root filesystem volume.
Although I am not sure, I do believe that the encryption scheme probably 
was not loopback (cryptoloop) because the server did not have a key 
stored on an external device. My understanding of loopback encryption is 
that the kernel and initrd have to be stored on at least some kind of 
un-encrypted media in order to boot to at least a small level sufficient 
to ask for the pass-key to decrypt/mount the filesystem.
If the encryption scheme wasn't loopback encryption, what could it have 
been? What ways are popular right now for encrypting an entire root 
filesystem without using a thumbdrive or other external storage??
If someone can help me identify what this was, maybe I can read up on it 
and implement it on one of my own servers.

Thanks in advance,
Jim Butler
Linux Network Administrator.