/ɛks tiː θriː/
noun — "journaling Linux filesystem."
EXT3, short for Third Extended File System, is a Linux filesystem that builds upon the structure of EXT2 by adding journaling capabilities to improve reliability and reduce recovery time after system crashes. It maintains backward compatibility with EXT2, allowing existing tools, utilities, and data to work seamlessly, while providing enhanced integrity for both metadata and optionally data.
Technically, EXT3 retains the block group organization of EXT2, where each block group contains inodes, data blocks, and bitmaps for free block and inode tracking. The key addition is the journal, a dedicated area that logs filesystem operations before they are committed. This journal can operate in multiple modes: writeback, which journals metadata only; ordered, which journals metadata and ensures data blocks are written before metadata; and journal, which logs both metadata and data for maximum consistency. EXT3 supports block sizes ranging from 1 to 4 kilobytes, enabling volumes up to multiple terabytes depending on block configuration.
Operationally, when a file is created or modified, the intended changes are first recorded in the journal. Once safely logged, the filesystem applies the changes to the main storage structures. If the system crashes unexpectedly, the journal can be replayed during the next mount to complete any pending operations, maintaining consistency without requiring full filesystem checks. Reading files involves accessing inodes to locate data blocks, similar to EXT2. Administrators can manage EXT3 with tools like tune2fs for adjusting filesystem parameters and fsck for integrity verification.
Example workflow for creating and mounting an EXT3 filesystem:
mkfs.ext3 /dev/sdb1
mount /dev/sdb1 /mnt/data
ls -l /mnt/data
This process formats a partition as EXT3, mounts it, and lists its contents, while journaling ensures rapid recovery if a crash occurs.
In practice, EXT3 is widely used in servers, desktops, and embedded Linux systems that need a balance between performance and reliability. Its backward compatibility simplifies upgrades from EXT2, while journaling reduces downtime caused by crashes. Although EXT4 offers newer features like extents and larger file support, EXT3 remains valued for stability and its proven track record.
Conceptually, EXT3 is like maintaining a ledger alongside your main document: intended edits are recorded in the ledger first, ensuring that even if the system fails, work can be completed without corruption.
See EXT2, EXT4, FileSystem, Journaling.