{
  "slug": "nvme-data-units-written",
  "term": "NVMe Data Units Written",
  "aliases": [
    "Data Units Written",
    "DUW",
    "data_units_written"
  ],
  "definition": "NVMe Data Units Written is the SMART / Health Information log counter of host-written data, excluding metadata, in rounded-up groups of 1,000 units of 512 bytes.",
  "note": "One reported unit corresponds to a 512000-byte quantum. For nonzero raw value v, multiplying v by 512000 gives the upper edge of the reporting bucket, not an exact byte total. Zero means the amount is not reported. Bytes 48 through 63 hold a 128-bit counter: preserve integer precision, for example with a decimal string or BigInt rather than an unrestricted JavaScript Number. [nvme-base-2-3-smart]",
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "Host writes are not physical NAND writes, so this counter alone cannot measure write amplification; interval differences also retain the rounding uncertainty of the two readings.",
      "citationIds": [
        "nvme-base-2-3-smart"
      ]
    }
  ],
  "related": [
    "nvme-smart-log",
    "nvme-percentage-used"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "nvme-base-2-3-smart",
      "title": "NVM Express Base Specification 2.3, section 5.2.12.1.3, Figure 210, p. 215: Data Units Written",
      "url": "https://nvmexpress.org/wp-content/uploads/NVM-Express-Base-Specification-Revision-2.3-2025.08.01-Ratified.pdf",
      "accessed": "2026-10-14"
    }
  ],
  "updated": "2026-10-14"
}