I have refined and updated my RAMboot how-to for Debian 8. Honestly, my previous how-to's still work fine for Debian 8, regardless of the switch to systemd. I have, however, tightened things up.
The basic concept is to boot from a local hard drive or USB drive, using a modified initrd to unpack ramboot/image.tar.gz to a tmpfs ramdisk. From then on, the system runs entirely from ram - uncompressed. This is like running off an extremely fast SSD, but with some important differences:...