{
  "slug": "unwritten-extent",
  "term": "Unwritten extent",
  "aliases": [
    "uninitialized extent"
  ],
  "definition": "An allocated filesystem extent whose data is not initialized and is exposed as zeros when read through the filesystem.",
  "note": "Unlike a hole it has allocation; unlike delayed allocation it has assigned storage. Zero reads do not establish device contents or sanitization.",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "file-extent",
    "file-preallocation",
    "sparse-file",
    "hole-punching"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-13",
  "citations": [
    {
      "id": "fiemap",
      "title": "Linux 6.12: FIEMAP extent states and access restrictions",
      "url": "https://docs.kernel.org/6.12/filesystems/fiemap.html",
      "accessed": "2026-10-13"
    },
    {
      "id": "hesela-allocation",
      "title": "Sparse files, preallocation and thin-pool capacity",
      "url": "https://hesela.com/analyses/sparse-files-preallocation-thin-capacity/",
      "accessed": "2026-10-13"
    }
  ]
}