It seems they're using xnbd to provide the storage for the box. On Debian, the box is running a xnbd-client, which provides the rootfs:

  xnbd-client --blocksize 4096 --retry=900 10.1.32.197 4096 /dev/nbd0

  root@scw-6d2eff:~# df -h
  Filesystem      Size  Used Avail Use% Mounted on
  /dev/nbd0        46G  507M   44G   2% /

I did not check, but I hope there's some filtering/authentication for that process.

Like EC2 and others, the box has an internal ip allocated and an external ip via nat (or something else).

I was able to download a file from OVH with ~500 Mbit/s throughput when writing to the filesystem. Writing to /dev/null it increases to ~650 Mbit/s.

Running an untuned nginx, it can do ~300 req/s with ~20% cpu util.

Seeing as the storage is still virtual, I'm not really sure why this would be so much better than a virtual machine. I like the idea though.