Journaling file system
Also known as: journaling, file system journal, transaction log file system
A journaling file system keeps a log (journal) of pending changes before writing them to disk, so an interrupted write — from a crash or power loss — can be rolled back or completed instead of leaving the drive corrupted. APFS, NTFS, ext4, and HFS+ all use journaling.
- Logs pending changes before writing them
- Recovers cleanly after a crash or power loss
- Used by APFS, NTFS, ext4, and HFS+
How journaling protects your files
When you save or move a file, the file system first records its intended changes in a small reserved area called the journal, then applies them to the disk, then marks the journal entry done. If the device loses power mid-write, the system replays or discards the journal on restart so the file structure stays consistent.
Without journaling, an interrupted write could leave a file half-updated and the directory pointing at garbage, the kind of corruption that once required long disk-check scans to repair. Journaling turns that into a quick, automatic recovery.
Where you already rely on it
Nearly every modern file system journals by design: APFS and the older HFS+ on Apple devices, NTFS on Windows, and ext4 on Linux and Android. You do not configure it — it runs in the background and you only benefit from it when a crash does not cost you data.
The journal itself uses a small, fixed amount of space and is not something you clear or manage; it is part of the cost of a reliable drive.