ext4-auto-da-alloc · shipping · also auto_da_alloc

Ext4 auto_da_alloc

Ext4 auto_da_alloc forces delayed block allocation for recognized file-replacement patterns to support ordered-mode crash protection.

Related Observatory article: Ext4 auto_da_alloc on hesela.com

The option covers selected replace-via-rename and replace-via-truncate patterns. Its documented protection depends on the next ordered-mode journal commit, not simply on close or rename returning. [1]

Linux v6.12 ext4_rename calls ext4_alloc_da_blocks when a destination inode exists and the option is enabled. Renaming to an absent destination does not take that branch. This narrow heuristic cannot replace an application's synchronization and error checks. [2] [3]

Relations

related
Delayed allocation, Ext4 ordered mode, Atomic rename, fsync, Directory fsync

Citations

  1. Linux v6.12: ext4 data modes and auto_da_alloc (accessed 2026-10-21)
  2. Linux v6.12: ext4_rename delayed-allocation condition (accessed 2026-10-21)
  3. Linux man-pages: fsync(2), file data, directory entries and errors (accessed 2026-10-21)
Sources & caveats
  • Source review scoped to Linux v6.12; not a crash experiment or certification of later kernels.

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Hesela team. Ext4 auto_da_alloc. Hesela. 2026-10-21. https://hesela.dev/terms/ext4-auto-da-alloc/