{
  "slug": "md-mismatch-count",
  "term": "MD mismatch count",
  "aliases": [
    "mismatch_cnt",
    "Linux MD mismatch counter"
  ],
  "definition": "Linux MD mismatch_cnt counts sectors rewritten, or that would be rewritten during check, when checking array redundancy.",
  "note": "Granularity: The accounting unit can exceed the actual damaged region. The mdadm 4.2 manual illustrates a failed 64 KiB comparison contributing 128 sectors, not proof that all 128 sectors differ. [md4]\n\nInterpretation: A mirror mismatch can involve unused or swap space rather than corrupted live file data. A mismatch alone does not identify the correct copy. Repair may make copies agree without independently establishing application correctness. [md4]\n\nCoverage: Retain the operation, checked range, progress and completion alongside the counter. A zero value alone does not establish a completed full-array scan; check is not guaranteed read-only for every RAID level. [md]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "data-scrubbing",
    "raid-1",
    "raid-5",
    "raid-6",
    "parity-inconsistency",
    "parity-pollution"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "md",
      "title": "Linux 6.18 documentation: RAID arrays, sync_action, mismatch_cnt and sync limits",
      "url": "https://docs.kernel.org/6.18/admin-guide/md.html",
      "accessed": "2026-10-22"
    },
    {
      "id": "md4",
      "title": "mdadm 4.2 md(4): scrubbing and mismatches",
      "url": "https://manpages.debian.org/bookworm/mdadm/md.4.en.html",
      "accessed": "2026-10-22"
    }
  ],
  "provenance": [
    "Documented Linux MD behavior; not a hardware measurement or a conversion from counter values to lost bytes."
  ],
  "updated": "2026-10-22"
}