{
  "slug": "random-io",
  "term": "Random I/O",
  "aliases": [
    "Random input/output",
    "Nonsequential I/O"
  ],
  "definition": "Random I/O is an access pattern in which successive requests do not consistently follow adjacent address ranges.",
  "note": "Meaning: Common usage describes a nonsequential workload, not necessarily a statistically random or uniform address distribution [snia].\n\nBenchmark setup: fio selects random reads or writes with rw=randread or rw=randwrite. Its random_distribution option defaults to uniform and also supports skewed distributions such as Zipf and Pareto [fio]. The word random alone does not specify request size, read/write mix, accessed range or achieved queue depth [fio].\n\nCoverage: In fio 3.39, the default random map avoids revisiting blocks within a coverage pass. norandommap removes that tracking; it does not guarantee independent sampling, because the chosen generator still matters. The lfsr generator avoids repeat offsets and requires a single block size. Selecting a nonuniform random_distribution disables the map [fio-sampling].",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "sequential-io",
    "io-request-size",
    "queue-depth",
    "iops",
    "throughput-storage",
    "ssd",
    "hdd",
    "posix-fadv-random"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "snia",
      "title": "SNIA Dictionary, 28 April 2026: random I/O and sequential I/O, pp. 244-245 and 270.",
      "url": "https://www.snia.org/sites/default/files/dictionary/SNIADictionary.pdf",
      "accessed": "2026-10-24"
    },
    {
      "id": "fio",
      "title": "fio documentation: rw, blocksize, random_distribution, iodepth and serialize_overlap.",
      "url": "https://fio.readthedocs.io/en/latest/fio_doc.html",
      "accessed": "2026-10-24"
    },
    {
      "id": "fio-sampling",
      "title": "fio 3.39 HOWTO: norandommap, random_generator and random_distribution.",
      "url": "https://raw.githubusercontent.com/axboe/fio/fio-3.39/HOWTO.rst",
      "accessed": "2026-10-24"
    }
  ],
  "provenance": [
    "The definitions are original paraphrases, not reproductions of SNIA Dictionary entries.",
    "The fio online manual was reviewed on 24 October 2026; option semantics describe a workload generator, not measured device performance."
  ],
  "updated": "2026-10-24"
}