System Administration Guide: Devices and File Systems

UFS Logging

UFS logging bundles the multiple metadata changes that comprise a complete UFS operation into a transaction. Sets of transactions are recorded in an on-disk log. Then, they are applied to the actual UFS file system's metadata.

At reboot, the system discards incomplete transactions, but applies the transactions for completed operations. The file system remains consistent because only completed transactions are ever applied. This consistency remains even when a system crashes. A system crash might interrupt system calls and introduces inconsistencies into a UFS file system.

UFS logging provides two advantages:

Logging is enabled by default for all UFS file systems, except under the following conditions:

In previous Solaris releases, you had to manually enable UFS logging.

Keep the following issues in mind when using UFS logging:

The UFS transaction log has the following characteristics:

If you need to enable UFS logging, specify the -o logging option with the mount command in the /etc/vfstab file or when you manually mount the file system. Logging can be enabled on any UFS file system, including the root (/) file system. Also, the fsdb command has new debugging commands to support UFS logging.

In some operating systems, a file system with logging enabled is known as a journaling file system.