Servers in a storage system store a nested multilayer directory structure, and a global index that is an abstract of the directory structure. The global index identifies respective portions of the directory structure that are stored in respective ones of the servers, and the global index identifies paths through the directory structure linking the respective portions. Upon performing a top-down search of the directory structure in response to a client request and finding that a portion of it is offline, the global index is searched to discover portions of the directory structure that are located below the offline portion. The global index may also identify the respective server storing each of the respective portions of the directory structure, and may indicate whether or not each of the respective portions of the directory structure is known to be offline.