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