journaling - TarisMajor/5143-OpSystems GitHub Wiki

Journaling is a technique used in file systems to maintain data integrity by keeping a record (journal) of changes that are made to files. This journal helps in recovering the file system to a consistent state in case of a crash or power failure. Journaling is crucial for modern file systems, ensuring data reliability and minimizing the risk of data corruption.

1. Transaction-Based: Changes to files are recorded as transactions in a separate journal before they are actually applied to the file system. This ensures that either all changes in a transaction are applied, or none are, maintaining consistency.
2. Logging Changes: The journal logs metadata changes, and optionally, the actual data changes. This log can be used to replay changes in case of a system failure.
3. Checkpointing: Periodically, the file system writes the logged changes from the journal to the main file system, creating a consistent checkpoint.

1. Data Integrity: Journaling ensures that the file system can recover to a consistent state after a crash, minimizing the risk of data corruption.
2. Fast Recovery: Since only the changes recorded in the journal need to be replayed, recovery is faster compared to non-journaling file systems that may require a complete file system check.
3. Efficient Crash Recovery: The ability to replay journal entries allows the file system to quickly restore itself without extensive scanning or repair operations.

1. Performance Overhead: Maintaining a journal adds some performance overhead due to additional write operations. However, this overhead is often outweighed by the benefits of quick and reliable recovery.
2. Additional Disk Space: The journal requires additional disk space, which can reduce the overall usable space on the storage device.
3. Complexity: Implementing journaling adds complexity to the file system design and operation.

1. Metadata Journaling: Only changes to the file system's metadata are logged. This provides a balance between performance and data integrity.
2. Full Data Journaling: Both metadata and actual data changes are logged. This offers the highest level of data protection but at the cost of increased performance overhead and disk space usage.
3. Ordered Journaling: Metadata changes are logged, and data changes are written to disk before the metadata is updated. This ensures a consistent state without the overhead of full data journaling.

1. Critical Systems: Ideal for critical systems where data integrity and quick recovery are paramount, such as database servers and financial systems.
2. Enterprise Environments: Useful in enterprise environments with large-scale storage systems where downtime and data loss can have significant impacts.
3. Personal Computers: Modern file systems like ext4 (Linux) and NTFS (Windows) implement journaling to ensure data reliability and user satisfaction.

• Operating System Concepts by Abraham Silberschatz, Peter B. Galvin, and Greg Gagne
• Journaling File Systems - GeeksforGeeks
• Modern Operating Systems by Andrew S. Tanenbaum
• Wikipedia - Journaling File System
• ChatGPT