ext4-data-journal · shipping · also ext4 data=journal, ext4 journal mode

Ext4 data journaling

Ext4 data journaling sends supported file contents and filesystem metadata through the journal before their final locations.

Related Observatory article: Ext4 data journaling on hesela.com

For ordinary unencrypted regular files, data=journal journals contents alongside metadata. When journaling would otherwise apply, Linux v6.12 instead selects ordered mode for fscrypt-encrypted regular files. The per-inode journal-data override requires disabled delayed allocation. [4] A filesystem transaction does not automatically match an application's multi-write or multi-file update. [1]

The Linux v6.12 guide states that this mode disables delayed allocation and O_DIRECT support. [2] The inode's data-journaling state makes ext4_dio_alignment return zero. [5] The write path then falls back to buffered I/O; its NOWAIT path rejects with EOPNOTSUPP, while earlier lock contention can yield EAGAIN. O_DIRECT alone does not verify page-cache bypass. [6]

Relations

related

Ext4 ordered mode, Ext4 writeback mode, Journal checkpoint, fsync, Crash consistency

Citations

1. Linux v6.12: journal coverage and ordered-mode fast commits (accessed 2026-10-21)
2. Linux v6.12: ext4 data modes and auto_da_alloc (accessed 2026-10-21)
4. Linux v6.12: ext4_inode_journal_mode, encrypted files and per-inode overrides (accessed 2026-10-21)
5. Linux v6.12: ext4_dio_alignment, data-journal exclusion (accessed 2026-10-21)
6. Linux v6.12: direct-I/O eligibility, buffered fallback and NOWAIT errors (accessed 2026-10-21)

Further reading

3. Linux man-pages: fsync(2), file data, directory entries and errors (accessed 2026-10-21)

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