{
  "slug": "nand-spare-area",
  "term": "NAND spare area",
  "aliases": [
    "NAND OOB",
    "NAND out-of-band area",
    "NAND page spare area"
  ],
  "definition": "The additional region associated with a NAND page, used for error-correction information, bad-block markers and other metadata according to a device- and controller-specific layout.",
  "note": "OOB means out-of-band relative to the page's main data, not a separate management bus. Linux MTD distinguishes ECC positions, reserved bad-block information and regions available for filesystem metadata; available bytes need not form one contiguous range. [mtd]\n\nDo not treat this as SSD over-provisioning or replacement blocks. It is per-page storage, and ECC requirements can constrain the space left for an FTL. [desnoyers]\n\nFor a raw-NAND image or boot-chain migration, record the page geometry, ECC scheme and OOB layout together. Preserve factory bad-block markers and follow the part's programming restrictions. A data-only dump does not by itself specify these details. This checklist is an engineering inference from the documented layout responsibilities. [mtd]",
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "A documented OOB layout is not a universal offset map for other NAND parts or controllers.",
      "citationIds": [
        "mtd"
      ]
    }
  ],
  "related": [
    "nand-flash",
    "nand-page",
    "nand-erase-block",
    "error-correcting-code",
    "bad-block-management",
    "ftl",
    "over-provisioning"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-18",
  "citations": [
    {
      "id": "mtd",
      "title": "Linux kernel. MTD NAND Driver Programming Interface: Bad block table support; Spare area (auto)placement; Filesystem support.",
      "url": "https://docs.kernel.org/driver-api/mtdnand.html",
      "accessed": "2026-10-18"
    },
    {
      "id": "desnoyers",
      "title": "Peter Desnoyers. What Systems Researchers Need to Know about NAND Flash. HotStorage 2013, section 3, Page spare areas.",
      "url": "https://www.usenix.org/system/files/conference/hotstorage13/hotstorage13-desnoyers.pdf",
      "accessed": "2026-10-18"
    }
  ],
  "provenance": [
    "Source review. The kernel document contains legacy API examples; this entry uses layout concepts, not its example byte offsets, page sizes or partial-program counts as current universal requirements. No device imaging or power-loss experiment was performed."
  ]
}