{
  "slug": "mttf-vs-field-replacement-rates",
  "title": "Field disk replacements averaged 3.01% a year, 3.4 times the 0.88% a 1,000,000-hour MTTF implies",
  "kind": "dataset",
  "summary": "Schroeder and Gibson, FAST 2007, report a weighted average annual replacement rate (ARR) of 3.01% for drives under five years old across seven field data sets (more than 100,000 drives, SCSI, FC, and SATA), 3.4 times the 0.88% annual failure rate implied by a datasheet MTTF of 1,000,000 hours. ARR counts replacements, not confirmed failures. Replacement rates kept rising with age (7 to 10 times the datasheet rate in years 4 and 5 of HPC1, up to 30 times for 5 to 8 year old systems), and time between replacements in HPC1 fits a Weibull shape of 0.71, not an exponential model. For scale, Pinheiro et al., FAST 2007, report 1.7% to over 8.6% AFR in a Google fleet, and Backblaze reports 1.73% for Q2 2026 and 1.41% lifetime.",
  "license": "Small derived table of figures printed in Schroeder and Gibson (FAST 2007), Pinheiro et al. (FAST 2007), and the Backblaze Q2 2026 Drive Stats post, with credit. Not a Creative Commons license. The USENIX proceedings page says rights to individual papers remain with the author or the author's employer. This file is not a copy of the papers, not the replacement logs, and not the Backblaze dataset. The Backblaze post asks that its raw Drive Stats data be cited and not resold, which this table does not redistribute.",
  "licenseUrl": "https://www.usenix.org/legacy/events/fast07/tech/schroeder.html",
  "sourceUrl": "https://www.usenix.org/legacy/events/fast07/tech/schroeder/schroeder_html/index.html",
  "accessed": "2026-10-09",
  "rowCount": 18,
  "columns": [
    { "name": "measure", "type": "string", "description": "The quantity as the source names it." },
    { "name": "value_low", "type": "number", "description": "Lower end of a printed range. Empty when the source prints a single value or an upper bound only." },
    { "name": "value_high", "type": "number", "description": "Single printed value, or the upper end of a printed range, or the upper bound for 'as much as' wording." },
    { "name": "unit", "type": "string", "description": "Unit of both value columns: percent of drives per year, times, or unitless." },
    { "name": "scope", "type": "string", "description": "Population and window the value applies to." },
    { "name": "note", "type": "string", "description": "What the value is not, or the source wording behind it." },
    { "name": "citation_id", "type": "string", "description": "Id of the opened source in the citations list." }
  ],
  "downloadPath": "/data/datasets/mttf-vs-field-replacement-rates.csv",
  "humanPage": "https://hesela.com/analyses/mttf-vs-field-replacement-rates/",
  "limits": [
    "ARR is drives replaced per year, not confirmed failures. The paper cites a vendor figure that 43% of returned disks show no problem.",
    "ARR per data set cannot be recomputed from the paper's Table 1 because disk counts changed and logs hold other events.",
    "Time-between-replacement, correlation, and Weibull figures are HPC1 only.",
    "Several results appear only as charts in the paper and are not in this file.",
    "Google age groups mix drive models. Backblaze figures are a different era and drive mix, and the opened post does not define a failure. Neither tests the 3.4 times ratio."
  ],
  "citations": [
    { "id": "schroeder-usenix-html", "title": "Disk failures in the real world: What does an MTTF of 1,000,000 hours mean to you?, Schroeder and Gibson, FAST 2007 (USENIX HTML proceedings)", "url": "https://www.usenix.org/legacy/events/fast07/tech/schroeder/schroeder_html/index.html", "accessed": "2026-10-09" },
    { "id": "schroeder-usenix-abstract", "title": "Disk Failures in the Real World, USENIX FAST 2007 abstract page", "url": "https://www.usenix.org/legacy/events/fast07/tech/schroeder.html", "accessed": "2026-10-09" },
    { "id": "pinheiro-usenix-html", "title": "Failure Trends in a Large Disk Drive Population, Pinheiro, Weber, and Barroso, FAST 2007 (USENIX HTML proceedings)", "url": "https://www.usenix.org/legacy/events/fast07/tech/full_papers/pinheiro/pinheiro_html/index.html", "accessed": "2026-10-09" },
    { "id": "backblaze-q2-2026", "title": "Backblaze Drive Stats for Q2 2026, published September 29, 2026", "url": "https://www.backblaze.com/blog/backblaze-drive-stats-for-q2-2026/", "accessed": "2026-10-09" }
  ]
}