{
  "slug": "dax",
  "term": "Direct Access",
  "aliases": [
    "DAX",
    "filesystem DAX"
  ],
  "definition": "Direct Access is a Linux mechanism that lets suitable memory-like storage serve file data without an intervening page-cache copy.",
  "note": "Filesystem DAX can map backing storage into userspace, but it does not by itself flush CPU caches or establish application crash consistency. The persistent FS_XFLAG_DAX preference and active S_DAX state are distinct; statx exposes the latter through STATX_ATTR_DAX. [dax-docs] MAP_SYNC adds a supported mapping guarantee used with appropriate CPU instructions, rather than making every store automatically durable. [mmap-docs]",
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "related": [
    "persistent-memory",
    "byte-addressable-storage",
    "map-sync",
    "persistence-domain"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-13",
  "citations": [
    {
      "id": "dax-docs",
      "title": "Linux kernel documentation. Direct Access for files: motivation and S_DAX state.",
      "url": "https://docs.kernel.org/filesystems/dax.html",
      "accessed": "2026-10-13"
    },
    {
      "id": "mmap-docs",
      "title": "Linux man-pages. mmap(2), MAP_SYNC and MAP_SHARED_VALIDATE.",
      "url": "https://man7.org/linux/man-pages/man2/mmap.2.html",
      "accessed": "2026-10-13"
    },
    {
      "id": "hesela-pmem",
      "title": "Hesela. Persistent memory: DAX is not a durable commit.",
      "url": "https://hesela.com/analyses/pmem-persistence-domains-dax/",
      "accessed": "2026-10-13"
    }
  ]
}