Write Path Sequence

%% Runtime view — the write path and its commit point %% Diagrams as code. Render with any Mermaid renderer. sequenceDiagram participant C as Client library participant Z as Placement / namespace (L2) participant L as Pending-chunk ledger participant D as D servers participant M as Metadata store (home zone) C->>Z: 0. Resolve/assign home zone (placement; cached) Z-->>C: home zone Note over C,M: Steps 1–4 run in the home zone. File does NOT exist yet C->>L: 1. Register chunk IDs (leased) C->>C: 2a. Chunk + erasure-code C->>D: 2b. Write fragments directly (parallel, bulk data) D-->>C: checksums verified Note over C,D: Fragments exist but are unreferenced garbage C->>M: 3. Atomic commit: chunk map + state=COMMITTED + version++ (conditional on prior version) Note over M: THIS is the commit point — the file now exists M-->>C: committed (or conflict → retry) C->>L: 4. Release ledger entries Note over C,M: Crash before 3 → leased garbage (GC). Crash 3→4 → custodian sweep.