The normative erasure-coding spec stated several target behaviors and known baseline defects as active invariants, and cited two symbols that do not exist on main. Each correction below was verified against the code.
- §4.1 shard size: legacy even-padding is RustFS-legacy-only and is NOT MinIO's sizing. MinIO (and the modern GF(2⁸) path) use plain div_ceil; for 1 MiB / 6 data shards that is 174763 bytes versus the legacy even-padded 174764. MinIO-migrated data is decoded by the modern path, so the legacy formula never applies to it.
- §6.3 / §11 MTime: the MTime key is always written (a None mod_time encodes as UNIX_EPOCH = 0), not omitted. Round-trip safety to None is enforced on the decode side, not by write omission. Only the legacy StatInfo.ModTime field is omitted-when-None.
- §7 commit: rollback after a missed write quorum is best-effort — undo failures are counted and warn!-logged, never propagated or retried — so a partially-failed rollback can leave shards behind; softened "never left partially committed" accordingly.
- §7 data_dir: reduce_common_data_dir votes over each disk's old_data_dir (a GC input for reclaiming the superseded dir), not the newly committed data_dir.
- §7 convergence: classify_rename_convergence is consumed only by the multipart-complete path (convergence.needs_heal()); the regular put_object path discards it.
- §7 write layout: removed the WriteLayout / resolve_write_layout citation — neither symbol exists on main (the write layout is computed inline), which violated the spec's own cite-real-symbols rule.
- §6.6 inline: inline presence is read from the meta_sys[inline-data] body marker alone; the header InlineData flag is written but not consulted on read, and disagreement is tolerated (MinIO may write the flag unset with inline data present). Removed the false "must agree" invariant.
- §11 UUID tolerance: version_id / data_dir (ID/DDir) decode as a fixed 16-byte Uuid::from_bytes and fail closed on a present-but-non-16-byte value; only transitioned-versionID uses the tolerant Uuid::from_slice(...).ok().filter(!nil). Split the previously-conflated bullet.
- §11 decode blanket: narrowed "everything else must degrade to a tolerant default" to enumerate the legitimate structural/geometry/version/length fail-closed guards (header array length, unknown header_ver, version > max, versions_len / bin_len bounds, non-16-byte ID/DDir).
- §8 / §13 codec guard: has_valid_dimensions() is a &self method, so it runs after construction and reliably covers only block_size == 0; a data_blocks == 0 geometry with parity > 0 panics in the .expect constructor before the guard runs. Noted the fallible-constructor fix.
Refuted and intentionally left unchanged: the "accepts container major == 1 with any minor" statement is correct — the reader compares only major (rejects major > 1) and never gates on minor, so minor 4 is accepted.
* docs(architecture): add normative erasure-coding algorithm and on-disk compatibility contract
Adds docs/architecture/erasure-coding.md as the source of truth for how RustFS erasure-codes, stores, reads, reconstructs, and heals user data, and the on-disk (xl.meta) / decode compatibility contract every future change must preserve. Grounded in the baseline (main) implementation with file:line anchors; cross-links (does not duplicate) the existing placement, MinIO-format-compat, layout-boundary, decommission, and tier-ILM docs, and the AGENTS.md cross-cutting invariants.
Covers: Reed-Solomon over GF(2^8) modern vs GF(2^16) legacy backends and how each is selected; pool/set/drive geometry with the 2..=16 set-size and per-pool parity invariants; the key-derived distribution permutation (1..=N); 1 MiB block size and the modern/legacy shard-size formulas; HighwayHash256S interleaved bitrot layout; the full xl.meta container/header/version-body schema and internal dual-key convention; write/read/heal quorum rules; and, newly codified as a first-class contract, the decode-tolerance invariants (nil-UUID/epoch-mod_time to None, skip unknown fields, hard-guard only length-critical arrays, tolerate the negative actual_size compressed sentinel, tolerate a malformed transitioned-versionID). Linked from the architecture README under "Contracts & invariants". Docs-only; check_doc_paths.sh passes.
* docs(architecture): anchor erasure spec by symbol name, not line numbers
Line numbers rot as code changes and are not validated by check_doc_paths.sh, so they would silently mislead the very code changes this normative spec is meant to guide. Replace all file:line citations with file-path + symbol-name references (functions/consts/types are greppable and rename only on deliberate changes; format byte offsets are kept). Add an explicit "references work here" note and a §13 rule that governed changes must update this spec in the same PR.
* docs(architecture): correct erasure spec after multi-expert adversarial review
Four independent adversarial reviewers fact-checked every claim against the code. Fixes:
- CRITICAL (found independently by two reviewers): §1 mislabeled the GF(2^16) reed-solomon-simd "legacy" backend as the reader for "older MinIO-lineage format". It is the opposite — that backend serves RustFS's own older main-branch (rmp_serde, uses_legacy_checksum) objects; MinIO-migrated data uses the same rs-vandermonde GF(2^8) scheme and is decoded by the modern backend. The old wording contradicted §1's own MinIO-interop line, §12, minio-file-format-compat.md, and the source comments, and would have misled the highest-stakes decode-routing decision.
- §2.1/§12: set size 2..=16 holds for multi-drive layouts; single-drive deployments run at N=1 (parity 0) outside is_valid_set_size.
- §2.2: validate_parity_inner enforces parity <= N/2 only for N > 2 (user storage-class parity flows through it); the standalone validate_parity is unconditional but only applied to the resolved default.
- §6.2/§12: header format is dispatched by header_ver; array length (4/5/7) is a per-version validation, not the discriminator.
- §6.3: the part-array length guard applies on the all_parts decode path.
- §6.5: get_bytes matches only the two canonical lowercase keys; only is_internal_key/get_str are case-insensitive.
- §6.5: transitioned-versionID — state the load-bearing invariant (non-16-byte decodes to None, never fatal); string-form recovery is optional, and transitioned-xl.meta interop is out of scope.
- §11: typo RustSF -> RustFS.
All other claims across §1-§14 were verified accurate against code (distribution formula, quorum formulas, on-disk key set/endianness/markers, decode-tolerance invariants, version anchors, standard references).
cxymds