> ## Documentation Index
> Fetch the complete documentation index at: https://docs.obsidianlog.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Local Backend

> The default, Sia-free backend: a filesystem store for development, testing, and offline use.

`LocalBackend` is the default: no Sia node, no wallet, nothing beyond disk.
`obsidianlog init` picks it unless you explicitly choose the Sia backend, and
every default build/test in this project runs against it, matching the
project's mock-first invariant.

## On-disk layout

Objects are stored as files under `<root>/<bucket>`, mirroring the same
layout used on Sia so the rest of the pipeline behaves identically
regardless of backend:

```text theme={null}
<root>/<bucket>/index/<service>/<window>-<sequence>.idx     # ServiceWindowIndex (JSON)
<root>/<bucket>/chunks/<service>/<window>-<sequence>.bin     # framed chunk (header + ciphertext)
<root>/<bucket>/manifest.json                                 # Manifest (JSON)
```

`sequence` (unique and monotonic per service) is part of the path, not just
`window`, since a window can legitimately receive many chunks over its lifetime
(one per batch that touches it), so `(service, window)` alone isn't a unique
storage location.

## Durability

Every write is durable and atomic: data is written to a temporary file in
the destination directory, `fsync`'d, then renamed into place, after which
the directory is `fsync`'d to persist the rename.

## When to use it

* Local development and testing.
* Offline or air-gapped environments.
* Anywhere you don't need Sia's durability/redundancy guarantees, or want to
  evaluate ObsidianLog before setting up a Sia backend at all.

For durable, redundant, off-site storage, see
[Hosted (Sia Storage)](/storage-backends/hosted-sia-storage) or
[Bring Your Own Indexer](/storage-backends/bring-your-own-indexer).