1. A method for migrating a non-overlapping portion of data from a source file storage node to a destination file storage node selected from one of an existing file storage node in a cluster of file storage nodes and a new file storage node added to the cluster, wherein each file storage node includes a file virtualization link identifying another file storage node for each of a plurality of non-overlapping portions not owned by the file storage node, the method comprising: updating a cluster resource to map the non-overlapping portion to the destination file storage node; establishing metadata for the non-overlapping portion on the destination file storage node; while establishing the metadata for the non-overlapping portion, servicing client requests received for the non-overlapping portion by the source file storage node based on a file virtualization link on the destination file storage node; after establishing the metadata for the non-overlapping portion on the destination file storage node, copying data for the non-overlapping portion from the source file storage node to the destination file storage node; while copying, servicing metadata requests received for the non-overlapping portion by the destination file storage node using the metadata and servicing data requests for the non-overlapping portion by the source file storage node based on the file virtualization link on the destination file storage node; and after completion of the copying, designating the destination file storage node as the owner of the non-overlapping portion.