dax · shipping · also DAX, filesystem DAX

Direct Access

Direct Access is a Linux mechanism that lets suitable memory-like storage serve file data without an intervening page-cache copy.

Related Observatory article: Direct Access on hesela.com

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. [1] MAP_SYNC adds a supported mapping guarantee used with appropriate CPU instructions, rather than making every store automatically durable. [2]

Relations

related

persistent-memory, byte-addressable-storage, map-sync, persistence-domain

Citations

1. Linux kernel documentation. Direct Access for files: motivation and S_DAX state. (accessed 2026-10-13)
2. Linux man-pages. mmap(2), MAP_SYNC and MAP_SHARED_VALIDATE. (accessed 2026-10-13)
3. Hesela. Persistent memory: DAX is not a durable commit. (accessed 2026-10-13)

JSON: /data/terms/dax.json