1. A method of operating a cluster of storage server nodes, the method comprising: mapping a given one of a plurality of filenames in a directory to a given one of the storage server nodes according to a first mapping, each storage server node services one of a plurality of persistent mass storage facilities; choosing an identifier of a meta-data container that stores meta-data attributes of the given filename, such that the identifier is mapped to the given storage server node according to a second mapping; distributing the directory, including the filenames and pointer information that points filenames to corresponding identifiers of corresponding meta-data containers, across the storage server nodes for storage on the persistent mass storage facilities according to the first mapping of the filenames; and in response to renaming the given filename to a second filename that is mapped to a different one of the storage server nodes according to the first mapping, moving the pointer information of the second filename to the different storage server node while retaining the meta-data attributes of the second filename on the given storage server node.