Upgrading the file system of objects in a distributed storage system

An example method of upgrading a distributed storage object from a first version to a second version includes: querying metadata of a first component configured according to the first version of the distributed storage object, the metadata defining extents of data on a disk group of the first component; populating, for a second component configured according to the second version of the distributed storage object, logical and middle maps based on the metadata such that initial entries in the logical map point to initial entries in the middle map, and the initial entries in the middle map point to physical addresses of the disk group of the first component; and reading the data from the disk group of the first component and writing the data to a disk group of the second component while updating the initial entries in the middle map.