# ASL/STORE-LAYOUT/1 -- On-Disk Store Layout

Status: Draft
Owner: Architecture
Version: 0.1.0
SoT: No
Last Updated: 2026-01-17
Tags: [ops, store, layout, filesystem]

**Document ID:** `ASL/STORE-LAYOUT/1`
**Layer:** O2 -- Operational layout profile

**Depends on (normative):**

* `ASL-STORE-INDEX`

**Informative references:**

* `ASL/HOST/1`

---

## 0. Conventions

The key words **MUST**, **MUST NOT**, **REQUIRED**, **SHOULD**, and **MAY** are to be interpreted as in RFC 2119.

ASL/STORE-LAYOUT/1 defines a recommended filesystem layout for an ASL store. It does not define semantic behavior.

---

## 1. Purpose

Provide a practical, POSIX-friendly on-disk layout that preserves ASL store semantics while remaining compatible with ZFS or other backends.

---

## 2. Minimum Required Components (Informative)

An ASL store requires:

* Immutable blocks
* Append-only log
* Sealed snapshots
* Deterministic replay

Directory layout is an implementation choice. This document defines a recommended layout.

---

## 3. Recommended Domain Layout

Per domain, use:

```
/asl/domains/<domain-id>/
  meta/
  blocks/
  index/
  log/
  snapshots/
  tmp/
```

All paths are domain-local.

---

## 4. Blocks

```
blocks/
  open/
    blk_<uuid>.tmp
  sealed/
    00/
      <blockid>.blk
    ff/
      <blockid>.blk
```

Rules:

* Open blocks are never visible.
* Sealed blocks are immutable.
* Sealed blocks are sharded by prefix for filesystem scalability.

---

## 5. Index Segments

```
index/
  shard-000/
    segment-0001.idx
    segment-0002.idx
    bloom.bin
  shard-001/
    ...
```

Rules:

* Segments are append-only while open.
* Sealed segments are immutable and log-visible.
* Shards are deterministic per snapshot.

---

## 6. Log and Snapshots

```
log/
  asl.log
snapshots/
  <snapshot-id>/
```

Rules:

* Log is append-only.
* Snapshots pin index and block state for replay.

---

## 7. Temporary and Metadata Paths

* `tmp/` is for transient files only.
* `meta/` contains domain metadata (DAM, policy, host state).

---

## 8. Non-Goals

ASL/STORE-LAYOUT/1 does not define:

* Device selection or mount options
* Snapshot mechanism (ZFS vs other)
* Encryption or key management