Storage server is read-only (no new uploads)
storage-server-policy blocked a write because the server is read-only (503).
Why this happens
Admin enabled read-only (drain before maintenance/migration). Existing files may still download; new uploads must go elsewhere.
Diagnose and fix
1. Admin: turn off read-only when uploads should resume, or select another writable server.
2. Finish transfers off the read-only node if draining.
3. Members: retry upload (selector should pick a writable server when available).
4. See No storage server is available for upload if every server is read-only/offline.