Journaling Versus Soft Updates: Asynchronous Meta-data Protection in File Systems
The UNIX Fast File System (FFS) is probably the most widely-used file
system for performance comparisons. However, such comparisons frequently
overlook many of the performance enhancements that have been added
over the past decade. In this paper, we explore the two most commonly
used approaches for improving the performance of meta-data operations
and recovery: journaling and Soft Updates. Journaling systems use an
auxiliary log to record meta-data operations and Soft Updates uses
ordered writes to ensure meta-data consistency.
The commercial sector has moved en masse to journaling file systems, as evidenced by their presence on nearly every server platform available today: Solaris, AIX, Digital UNIX, HP-UX, Irix, and Windows NT. On all but Solaris, the default file system uses journaling. In the meantime, Soft Updates holds the promise of providing stronger reliability guarantees than journaling, with faster recovery and superior performance in certain boundary cases.