storePath as a settable property of derivation

[veprbl]

Is your feature request related to a problem? Please describe.
I would like to store semi-large pieces of data in the Nix store. In a typical HPC environment there would be different filesystems for storing lots of small files (NFS/AFS with limited quota) and for storing large files (GPFS/Ceph with block size 256KiB or more).

Describe the solution you'd like
Would be nice to be able to define derivations that produce an output into a custom store path:

derivation {
  name = "data";
  # ...
  storePath = /mnt/disk;
}

This is already partially working in a sense that an existing Nix installation can be run with different values of NIX_STORE_DIR and the same value of NIX_STATE_DIR.

Describe alternatives you've considered
The alternative is to store symlinks in the store

stdenv.mkDerivation {
  # ...
  installPhase = ''
    out_data="/mnt/disk/$(basename $out)"
    mv data "$out_data"
    ln -s "$out_data" "$out"
  '';
}

Lacks most of the benefits: proper garbage collection, sandboxing support, etc.

Possible overlap with #5025

[Ericson2314]

I am also reminded of how different remote builders can have different "features" to ensure that certain derivations go just to then.

I think that + a union store that does a bind mount is the right way to do this.

[stale]

I marked this as stale due to inactivity. → More info

[veprbl]

Still wanted

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/super-colliding-nix-stores/28462/11

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/install-some-nix-packages-to-other-location-than-nix-store/30770/12