1fab06d851
Add a bit more information, callouts to prevent people potentially bricking their laptops. Also change the performance section, we will Change-Id: Id516c4bb0f0c2cbe99db86199b91c7d68becdd44 Reviewed-on: https://cl.snix.dev/c/snix/+/30254 Autosubmit: Florian Klink <flokli@flokli.de> Tested-by: besadii Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>
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| title | description | date | lastmod | draft | weight | categories | tags | contributors | pinned | homepage |
|---|---|---|---|---|---|---|---|---|---|---|
| Snix as lower Nix Overlay Store | How to use Snix as your lower Nix Overlay Store | 2025-03-21T22:40:33+00:00 | 2025-03-21T22:40:33+00:00 | false | 51 | false | false |
Background
About a year ago, Nix introduced a new experimental store type: [Local Overlay Store]. This store allows having multiple physical stores acting as a single logical store.
With this approach, stores are layered on top of each other with all but the top-most layer being writable, the others are read-only. Nix will build inside the top-most layer. The feature is described in the [Upstream Nix Documentation][Local Overlay Store]. Work is [ongoing][lix-local-overlay] to bring the feature to Lix aswell.
The main use-case is for it is having a large Nix store mounted onto a machine as read-only and having Nix not rebuild/substitute store paths available in lower layers.
Due to implementation details of this feature, the lower layer(s) can not only
be a location on the file system but also have another nix-daemon back the
lower layer(s).
Meet the new snix nix-daemon
Implementing nix-daemon protocol is a lot of effort, due to being entirely
custom and undocumented. On the other hand, mounting a large nix store is a
great fit for snix as our [content-addressed store][castore] is much more
space efficient than conventional filesystem storage. A great example of this
can be found [here][replit].
What's interesting about Local Overlay Store, is that it uses only a small
subset of operations when talking to the nix-daemon. And this seemed like a
good opportunity to make using nix backed by our castore more seamless.
So we are happy to announce that as of today, snix has implemented all of
the operations required to operate as a lower layer in nix's overlay store.
Check out our [Guide]({{< ref "/docs/guides/local-overlay.md" >}}) on how to set it up.
Please test it out, let us know what you think and report [bugs].
What's next for Local Overlay Store
We have plans expand our nix-daemon to support non-readonly mode and have all
possible substitutions go into your local castore and only use the upper nix
store for local builds.
We also want to make snix nix-daemon easier to use without having to run
multiple snix components.
Stay tuned.
[castore]: {{< ref "/docs/components/overview.md" >}} [bugs]: https://git.snix.dev/snix/snix/issues [Local Overlay Store]: https://nix.dev/manual/nix/2.26/store/types/experimental-local-overlay-store.html [replit]: https://blog.replit.com/tvix-store [lix-local-overlay]: https://gerrit.lix.systems/c/lix/+/2859