journaling filesystem
also: journaled filesystem, journaling
A filesystem that maintains a journal (log) of changes before committing them to disk, allowing rapid recovery from unexpected shutdowns or crashes without lengthy disk checks.
A journaling filesystem keeps a log of pending changes in a special journal area before writing them to the actual filesystem. If the system crashes or loses power mid-operation, the journal allows the filesystem to quickly replay or rollback incomplete transactions and return to a consistent state.
Without journaling, recovering from a crash requires running fsck (filesystem check), which scans the entire disk—a process that can take hours on large drives. Journaling filesystems like ext3, ext4, XFS, and Btrfs reduce recovery time to seconds by replaying the journal.
For example, when you save a file, the journal first records "write file X to blocks 100-105," then updates the inode table, then marks blocks as used. If power fails between steps, the journal knows exactly what was in progress and can complete or undo it safely.