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The '''Smart File System''' ('''SFS''') is a [[journaling filesystem]] used on [[Amiga]] computers. It is designed for performance, [[scalability]] and integrity. It uses block sizes ranging from 512 (2<sup>9</sup>) to 32768 (2<sup>15</sup>) [[byte]]s with a maximum partition size of 128 GB.
Good performance of the filesystem is realized by grouping multiple directory entries into a single block and by grouping meta data blocks together into clusters. A [[free space bitmap|bitmap]] is used to keep track of free space, and file data is kept track of using extents arranged into a [[B-tree|B+ tree]] structure.
Integrity is maintained by keeping a [[rollback log]] of all changes made to metadata over a certain period of time. The log is written to disk first into free space and then meta data blocks are overwritten directly. Should the system crash, the next time the filesystem is mounted it will notice the uncompleted operation and roll it back to the last known consistent state. For performance reasons, only metadata integrity is ensured. Actual data in files can still be corrupted if a write operation is terminated half way through.
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