Abstract: A device and method for providing a fault-tolerant file system. The fault-tolerant file system attempts to minimize the number of writes used when updating file system data structures. In one embodiment, file system data, including file system metadata, is stored in a fault-tolerant tree including a working state and a transacted state. In one embodiment, a change list is used to track blocks that have been updated, instead of cascading updates to leaf nodes up the tree, and a delta block is used to further minimize block updates when adding or removing nodes from the tree. In one embodiment, a Q-Block is used to prevent cycles when adding and removing free blocks from an allocation tree. Metadata values are stored in the tree in a way that allows certain metadata values to be inferred when not present in the tree, thus conserving space and lowering query time.