Optimizing file system resource reservation is presented herein. The method comprises dividing a virtual file system address space into subspaces, initializing the subspaces with volume slices of a group of volume slices comprising a first volume slice, a second volume slice, and a collection of reserved volume slices allocated based on an allocation pattern that allocates volume slices as a function of a quantitative relationship between a first value associated with a first volume slice and a second value associated with a second volume slice, determining that a data block count is insufficient to service a write operation of user data to the second volume slice; and provisioning a second subspace with a free volume slice obtained from the collection of reserved volume slices, and wherein the provisioning of the second subspace with the free volume slice is performed without invoking a memory exclusion mechanism.