{
  "slug": "optimal-io-size",
  "term": "Optimal I/O size",
  "aliases": [
    "optimal_io_size",
    "OPT-IO",
    "io_opt"
  ],
  "definition": "Optimal I/O size is a Linux block-layer hint for the preferred request unit for sustained I/O, expressed in bytes.",
  "note": "Zero means no optimum was reported, not that zero-length requests are useful. Treat the value as a workload starting point, not a measured best size for every application. [linux-abi]",
  "advantages": [
    {
      "text": "The blockdev --getioopt query can record the hint without issuing a data write.",
      "citationIds": [
        "blockdev"
      ]
    }
  ],
  "limitations": [
    {
      "text": "For partitions, lsblk can inherit queue attributes from the parent, so matching rows are not independent device measurements.",
      "citationIds": [
        "lsblk"
      ]
    }
  ],
  "related": [
    "minimum-io-size",
    "alignment-offset",
    "partition-alignment",
    "physical-sector"
  ],
  "provenance": [
    "Linux v6.12 ABI and util-linux v2.40.2 manuals define the scope; no universal throughput gain is claimed."
  ],
  "citations": [
    {
      "id": "linux-abi",
      "title": "Linux 6.12: stable sysfs block ABI, sector sizes and I/O topology",
      "url": "https://raw.githubusercontent.com/torvalds/linux/v6.12/Documentation/ABI/stable/sysfs-block",
      "accessed": "2026-10-19"
    },
    {
      "id": "blockdev",
      "title": "util-linux 2.40.2: blockdev query options and byte units",
      "url": "https://raw.githubusercontent.com/util-linux/util-linux/v2.40.2/disk-utils/blockdev.8.adoc",
      "accessed": "2026-10-19"
    },
    {
      "id": "lsblk",
      "title": "util-linux 2.40.2: lsblk explicit columns and inherited queue attributes",
      "url": "https://raw.githubusercontent.com/util-linux/util-linux/v2.40.2/misc-utils/lsblk.8.adoc",
      "accessed": "2026-10-19"
    },
    {
      "id": "hesela-sector-alignment",
      "title": "Hesela: 512e, 4Kn and alignment: geometry is not durability",
      "url": "https://hesela.com/analyses/sector-sizes-alignment-not-durability/",
      "accessed": "2026-10-19"
    }
  ],
  "status": "shipping",
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-19"
}