NBD is a protocol for accessing Block Devices (actual hard disks, and things that look like hard disks). nbdkit is a toolkit for creating NBD servers.
You can now write nbdkit plugins in Ruby.
(So in all that makes: C/C++, Perl, Python, OCaml or Ruby as your choices for nbdkit plugins)
Richard WM Jones 
I wish I had this an year ago. Quite useful anyway! Thanks.