{
  "slug": "annual-replacement-rate",
  "term": "Annual replacement rate",
  "aliases": [
    "ARR"
  ],
  "definition": "Annual replacement rate (ARR) counts recorded device replacements relative to device exposure, scaled to one year.",
  "note": "For exposure E in drive-years and R recorded replacements, 100 R/E expresses replacements per 100 drive-years. Declare the replacement policy: a replacement record does not certify a physical failure. Do not substitute an end-of-period headcount for exposure when the fleet changes.",
  "related": [
    "afr",
    "drive-day",
    "interarrival-time",
    "mtbf"
  ],
  "citations": [
    {
      "id": "schroeder-arr",
      "title": "Schroeder and Gibson, FAST 2007: Disk failures in the real world, sections 2.1-2.3",
      "url": "https://static.usenix.org/events/fast07/tech/schroeder/schroeder_html/index.html",
      "accessed": "2026-10-12"
    },
    {
      "id": "hesela-measurement-clocks",
      "title": "Hesela: Disk replacement rates are not disk lifetimes",
      "url": "https://hesela.com/analyses/mttf-vs-field-replacement-rates/",
      "accessed": "2026-10-12"
    }
  ],
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-12"
}