{
  "slug": "raidshield-reallocated-sectors",
  "title": "Replacing disks at 200 reallocated sectors removed 88% of triple-disk RAID failures at one vendor",
  "kind": "dataset",
  "summary": "Ma et al., FAST 2015, analysed about 1 million SATA disks in 6 models in one vendor's backup systems (logs of 21 to 60 months from June 2008). Replacing a disk once its reallocated-sector count passed 200 avoided about 88% of triple-disk RAID failures, which were 80% of RAID failures, or about 70% of all disk-related incidents. In simulation, thresholds below 200 caught 52% to 70% of failures within 60 days with 0.8% to 4.5% false positives. Cross-check rows come from Google (FAST 2007) and Backblaze (2016).",
  "license": "Small derived table of figures printed in Ma et al. (FAST 2015), Pinheiro et al. (FAST 2007), and a Backblaze post of 6 October 2016, with credit. Not a Creative Commons license. The USENIX proceedings state that rights to individual papers remain with the author or the author's employer. This file is not a copy of the papers and not the underlying logs.",
  "licenseUrl": "https://www.usenix.org/system/files/conference/fast15/fast15-paper-ma.pdf",
  "sourceUrl": "https://www.usenix.org/system/files/conference/fast15/fast15-paper-ma.pdf",
  "accessed": "2026-10-10",
  "rowCount": 17,
  "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."
    },
    {
      "name": "value_high",
      "type": "number",
      "description": "Single printed value, or the upper end of a range. For 'more than half' it is the stated bound."
    },
    {
      "name": "unit",
      "type": "string",
      "description": "Unit of the value columns: disks, blocks, files, percent of disks, percent of mismatches, or probability."
    },
    {
      "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/raidshield-reallocated-sectors.csv",
  "humanPage": "https://hesela.com/analyses/raidshield-reallocated-sectors/",
  "limits": [
    "The 88% is the vendor's own before and after comparison, normalized to the pre-deployment monthly average. Absolute rates are not published.",
    "The deployed rule covered 3 of the 6 models. Simulated rates come from one model.",
    "The paper prints 65% and 2.5% in the introduction and 52% to 70% and 0.8% to 4.5% in the evaluation.",
    "ARMOR was only simulated.",
    "The systems are write-heavy backup systems.",
    "Google and Backblaze rows are different fleets and measures and do not test the 88%."
  ],
  "citations": [
    {
      "id": "ma-fast15-pdf",
      "title": "RAIDShield: Characterizing, Monitoring, and Proactively Protecting Against Disk Failures, Ma et al., FAST 2015 (USENIX PDF)",
      "url": "https://www.usenix.org/system/files/conference/fast15/fast15-paper-ma.pdf",
      "accessed": "2026-10-10"
    },
    {
      "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-smart-2016",
      "title": "What SMART Stats Tell Us About Hard Drives, Backblaze, 6 October 2016",
      "url": "https://www.backblaze.com/blog/what-smart-stats-indicate-hard-drive-failures/",
      "accessed": "2026-10-10"
    }
  ]
}