{
  "slug": "mean-latent-error-time",
  "term": "Mean latent error time",
  "aliases": [
    "MLET",
    "Latent error time",
    "LET"
  ],
  "status": "research",
  "definition": "Mean latent error time (MLET) is the expected fraction of a drive's operating horizon during which at least one latent sector error remains undetected.",
  "note": "Oprea and Juels define LET for one error history and MLET as its mean over the error-model distribution; both are dimensionless. [oprea]\n\nOverlapping undetected intervals contribute once to exposed time, while an event-mean detection delay counts each event separately. In Hesela's ten-hour example, the same two onsets can yield LET of 40%, 50% or 60%; the respective mean delays are 3, 2.5 and 3 hours. These are invented complete histories, not a fitted MLET or a comparison at equal I/O cost. Detection ends the undetected state, not necessarily the need for repair. [hesela-exposure]\n\nThe trace-based FAST 2010 comparison uses MTTED and addresses uncertainty in fault-onset timestamps. Preserve the population, horizon, detection rules and censoring when comparing either metric. [schroeder]",
  "related": [
    "mean-time-to-detection",
    "staggered-scrubbing",
    "latent-sector-error",
    "data-scrubbing"
  ],
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-20",
  "citations": [
    {
      "id": "oprea",
      "title": "Oprea and Juels. A Clean-Slate Look at Disk Scrubbing. FAST 2010, section 5.",
      "url": "https://www.usenix.org/legacy/events/fast10/tech/full_papers/oprea.pdf",
      "accessed": "2026-10-20"
    },
    {
      "id": "schroeder",
      "title": "Schroeder, Damouras and Gill. Understanding latent sector errors and how to protect against them. FAST 2010, section 5.1.",
      "url": "https://www.usenix.org/legacy/events/fast10/tech/full_papers/schroeder.pdf",
      "accessed": "2026-10-20"
    },
    {
      "id": "hesela-exposure",
      "title": "Hesela: LET interval union versus event-mean detection delay.",
      "url": "https://hesela.com/analyses/scrubbing-detection-not-durability/#latent-exposure",
      "accessed": "2026-10-20"
    }
  ]
}