{
  "slug": "raid-1",
  "term": "RAID 1",
  "aliases": [
    "RAID1"
  ],
  "definition": "RAID 1 stores a full copy of each logical block on multiple storage members.",
  "note": "Copies: A single N-way mirror with N equal-sized members of capacity S provides ideal data capacity S, before overhead. Two-way mirroring uses half the aggregate member capacity, but a three-way mirror uses one third. [c1] [capacity]\n\nSurvival: One current, readable full copy can retain the data after other members fail. Array assembly, consistency and the availability of its controller and paths still matter. A stale or incomplete member is not interchangeable with a synchronized copy. [capacity] [md4]\n\nRecovery: Mirrored writes also propagate unwanted overwrites. RAID 1 does not by itself preserve a historical recovery point. Conventional paired RAID 10 combines multiple mirror groups with striping, rather than keeping a full array copy on every member. [protection] [raid10]\n\nReads: Linux MD balances reads among members, but its documented single sequential stream does not gain the striping benefit of RAID 0. Concurrent streams or random reads can use multiple members; mirrored writes update the active copies. [md4]\n\nSynchronization: By default, mdadm starts an initial resync when creating a RAID 1 array. With optional write-behind enabled, Linux MD can report write completion before designated write-mostly members have caught up. Member count alone does not prove that every copy is current. [mdadm] [md4]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "raid",
    "mirroring",
    "mirror-set",
    "raid-0",
    "raid-10",
    "degraded-array",
    "backup",
    "md-mismatch-count"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "c1",
      "title": "SNIA dictionary: RAID 1",
      "url": "https://www.snia.org/education/online-dictionary/term/raid-1",
      "accessed": "2026-10-20"
    },
    {
      "id": "capacity",
      "title": "Red Hat Enterprise Linux 10: Managing RAID, section 16.3",
      "url": "https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/10/html/managing_storage_devices/managing-raid",
      "accessed": "2026-10-20"
    },
    {
      "id": "md4",
      "title": "mdadm 4.2 md(4): RAID1 and array recovery",
      "url": "https://manpages.debian.org/bookworm/mdadm/md.4.en.html",
      "accessed": "2026-10-20"
    },
    {
      "id": "protection",
      "title": "SNIA Data Protection Best Practices (2025), sections 7.1 and 7.2.3",
      "url": "https://www.snia.org/sites/default/files/2025-03/SNIA-Data-Protection-Best-Practice-2025-01-27-v2.pdf",
      "accessed": "2026-10-20"
    },
    {
      "id": "raid10",
      "title": "SNIA dictionary: RAID 10",
      "url": "https://www.snia.org/education/online-dictionary/term/raid-10",
      "accessed": "2026-10-20"
    },
    {
      "id": "mdadm",
      "title": "mdadm 4.2: create, resync and write-behind",
      "url": "https://manpages.debian.org/bookworm/mdadm/mdadm.8.en.html",
      "accessed": "2026-10-22"
    }
  ],
  "updated": "2026-10-22"
}