add in-place mode for installation on hosts with small RAM

[wucke13]

I found myself in a position to provision a vhost that can't physically fit its entire store in RAM. It was not practical to push the pre-build image to that host. The host only has one disk, which is the install disk.

Under these circumstances, I see no other way but to use the target disk in-place for the fetching of all packages (instead of pref-etching to the install images tmpfs backed /nix/store).

[ophilli]

Just for context - how small is your RAM where this is necessary?

[wucke13]

2 gigabyte in that case

[Mic92]

I assume you are talking about disko-install?