{
  "slug": "backblaze-2025-monthly-afr",
  "title": "Backblaze hard drive AFR by month and capacity class, 2025",
  "kind": "dataset",
  "summary": "Month-by-month annualized failure rate of Backblaze's hard drives in 2025 (January 1 to December 31), computed from the raw daily Drive Stats files with exact 95% Poisson intervals, for all drives of 3 TB or more and for three capacity classes. Sample: 115,936,784 drive days and 4,327 failures, a 1.36% pooled AFR that matches Backblaze's published annual figure. Monthly AFR runs from 0.54% in December to 1.72% in September. One fleet, one year, and the file does not say why months differ.",
  "license": "Derivative table computed from the Backblaze Drive Stats daily files for 2025. Cite Backblaze if you use it. You are solely responsible for how you use it. Backblaze's dataset page allows sale of derivative works and forbids selling the Drive Stats data itself. This CSV is a 52-row aggregate, not the daily SMART archive, and that archive is not for sale.",
  "licenseUrl": "https://www.backblaze.com/cloud-storage/resources/hard-drive-test-data",
  "sourceUrl": "https://www.backblaze.com/cloud-storage/resources/hard-drive-test-data",
  "accessed": "2026-10-10",
  "rowCount": 52,
  "columns": [
    {
      "name": "month",
      "type": "string",
      "description": "Calendar month 2025-01 to 2025-12, or \"2025 total\" for the sum of the twelve months."
    },
    {
      "name": "size_class",
      "type": "string",
      "description": "All hard drives of 3 TB or more, or a nominal capacity class: up to 12 TB, 14 to 16 TB, 20 TB and above (round(capacity_bytes / 1e12))."
    },
    {
      "name": "drive_days",
      "type": "integer",
      "description": "Daily rows (drive days) of the class in the month. This is the exposure."
    },
    {
      "name": "failures",
      "type": "integer",
      "description": "Rows with failure = 1 in the month."
    },
    {
      "name": "afr_percent",
      "type": "number",
      "description": "failures / drive_days * 365 * 100, two decimals. Computed here, with 365 days in every month."
    },
    {
      "name": "afr_low95",
      "type": "number",
      "description": "Lower bound of the exact two-sided 95% Poisson (Garwood) interval, in percent."
    },
    {
      "name": "afr_high95",
      "type": "number",
      "description": "Upper bound of the same interval, in percent."
    }
  ],
  "downloadPath": "/data/datasets/backblaze-2025-monthly-afr.csv",
  "chartPath": "/data/datasets/backblaze-2025-monthly-afr.svg",
  "citations": [
    {
      "id": "bb-data-Q1",
      "title": "Backblaze Hard Drive Test Data, data_Q1_2025.zip (daily CSV files)",
      "url": "https://f001.backblazeb2.com/file/Backblaze-Hard-Drive-Data/data_Q1_2025.zip",
      "accessed": "2026-10-11"
    },
    {
      "id": "bb-data-Q2",
      "title": "Backblaze Hard Drive Test Data, data_Q2_2025.zip (daily CSV files)",
      "url": "https://f001.backblazeb2.com/file/Backblaze-Hard-Drive-Data/data_Q2_2025.zip",
      "accessed": "2026-10-11"
    },
    {
      "id": "bb-data-Q3",
      "title": "Backblaze Hard Drive Test Data, data_Q3_2025.zip (daily CSV files)",
      "url": "https://f001.backblazeb2.com/file/Backblaze-Hard-Drive-Data/data_Q3_2025.zip",
      "accessed": "2026-10-11"
    },
    {
      "id": "bb-data-Q4",
      "title": "Backblaze Hard Drive Test Data, data_Q4_2025.zip (daily CSV files)",
      "url": "https://f001.backblazeb2.com/file/Backblaze-Hard-Drive-Data/data_Q4_2025.zip",
      "accessed": "2026-10-11"
    },
    {
      "id": "bb-terms",
      "title": "Backblaze Hard Drive Test Data page and use terms",
      "url": "https://www.backblaze.com/cloud-storage/resources/hard-drive-test-data",
      "accessed": "2026-10-11"
    },
    {
      "id": "bb-2025",
      "title": "Backblaze Drive Stats for 2025 (published annual table: 115,638,676 drive days, 4,317 failures, 1.36%)",
      "url": "https://www.backblaze.com/blog/backblaze-drive-stats-for-2025/",
      "accessed": "2026-10-11"
    },
    {
      "id": "garwood",
      "title": "Garwood, F. (1936). Fiducial limits for the Poisson distribution. Biometrika 28(3-4), 437-442",
      "url": "https://doi.org/10.1093/biomet/28.3-4.437",
      "accessed": "2026-10-11"
    }
  ]
}