{
  "slug": "file-extent",
  "term": "File extent",
  "aliases": [
    "filesystem extent"
  ],
  "definition": "A filesystem mapping for a contiguous range of file blocks and the storage blocks backing that range.",
  "note": "Ext4 stores a starting file block, storage block and length for each extent, reducing mapping metadata for contiguous runs; this is a filesystem representation, not a statement about physical NAND placement.",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "unwritten-extent",
    "sparse-file",
    "file-preallocation",
    "reflink"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-13",
  "citations": [
    {
      "id": "ext4-extents",
      "title": "Linux 6.12: ext4 extent tree and mapping format",
      "url": "https://docs.kernel.org/6.12/filesystems/ext4/dynamic.html#extent-tree",
      "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"
    }
  ]
}