{
  "slug": "nvme-unexpected-power-losses",
  "term": "NVMe Unexpected Power Losses",
  "aliases": [
    "Unexpected Power Losses",
    "UPL",
    "NVMe Unsafe Shutdowns",
    "Unsafe Shutdowns",
    "unsafe_shutdowns"
  ],
  "definition": "NVMe Unexpected Power Losses is the SMART / Health Information log counter of main-power losses that meet the specification's incomplete-shutdown conditions.",
  "note": "Formerly named Unsafe Shutdowns, the field counts power loss before the controller reports ready to be powered off (CSTS.SHST = 10b), plus specified out-of-band Admin-command cases in which Ignore Shutdown permits media access during or after shutdown processing. NVMe Base 2.3 places it at bytes 144 through 159. Its definition is not limited to a missing CC.SHN notification; readiness and media shutdown state matter. [nvme-base-2-3-smart]",
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "This is a power-loss event count, not a count of corrupted files: an increase does not by itself prove data loss or identify its cause, while unprotected systems may suffer corruption.",
      "citationIds": [
        "nvme-changes-2-1",
        "nvme-base-2-3-smart"
      ]
    }
  ],
  "related": [
    "nvme-smart-log",
    "nvme-media-data-integrity-errors",
    "nvme-error-information-log-entries"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "nvme-changes-2-1",
      "title": "Changes in NVM Express Specifications (August 2024), section 1.2.23.1, p. 15: rename and revised counting conditions",
      "url": "https://nvmexpress.org/wp-content/uploads/NVM-Express-Revision-2.1-Changes-08_07.pdf",
      "accessed": "2026-10-14"
    },
    {
      "id": "nvme-base-2-3-smart",
      "title": "NVM Express Base Specification 2.3, section 5.2.12.1.3, Figure 210, p. 216: Unexpected Power Losses",
      "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"
}