[Nix-dev] disk setup for nixos installation

[Tim Barbour]

On further reflection, I think I see how it almost might work using
derivations.  Assume it is possible to have a derivation that is only
considered to be built (hand-waving part here ...) if the required filesystem
exists. Then that derivation depends on another that is only considered to be
built if the necessary LVM volume exists, etc. . I still cannot see how to
make the hand-waving part referentially transparent.

I think nixos must have a solution to this problem, otherwise how can it
install GRUB ?

Tim