{
  "slug": "fios",
  "term": "FIOS",
  "aliases": [
    "Fair, Efficient Flash I/O Scheduler",
    "FIOS scheduler"
  ],
  "definition": "FIOS is a research operating-system I/O scheduler combining per-task time budgets, optional read preference, concurrent dispatch and anticipation for flash-storage fairness.",
  "note": "Unused timeslice survives task switches within an epoch. An exhausted task waits for renewal; fairness over that epoch is not a per-request latency guarantee. [fios] [flashfq]\n\nOptional read preference can withhold writes while reads remain outstanding, but cannot preempt an already dispatched write. The authors allow disabling it when read/write interference is modest. [fios]",
  "status": "research",
  "advantages": [],
  "limitations": [
    {
      "text": "The historical Linux prototype changed filesystem behavior and disabled journaling; it is not a contemporary NVMe performance ranking.",
      "citationIds": [
        "fios"
      ]
    }
  ],
  "related": [
    "io-scheduler",
    "anticipatory-scheduling",
    "flashfq"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-11-08",
  "citations": [
    {
      "id": "fios",
      "title": "Park and Shen. FIOS: A Fair, Efficient Flash I/O Scheduler. FAST 2012, sections 4.1-4.4 and 5.",
      "url": "https://static.usenix.org/events/fast12/tech/full_papers/Park.pdf",
      "accessed": "2026-11-08"
    },
    {
      "id": "flashfq",
      "title": "Shen and Park. FlashFQ. USENIX ATC 2013, sections 3 and 6.",
      "url": "https://www.cs.rochester.edu/u/kshen/papers/usenix2013-shen.pdf",
      "accessed": "2026-11-08"
    },
    {
      "id": "hesela",
      "title": "Hesela: Sharing an SSD: who pays for the slowdown?",
      "url": "https://hesela.com/analyses/ssd-fairness-shared-queues/",
      "accessed": "2026-11-08"
    }
  ],
  "provenance": [
    "Primary-source synthesis; no scheduler implementation, hardware benchmark or performance replication was performed."
  ]
}