A method in a computer system, the method comprising: providing an object store which stores objects (200, 205, 220), wherein the object store internally manages and accesses the objects (200, 205, 220) using a flat namespace that maps unique identifiers to the stored objects (200, 205, 220), and wherein the object store stores the objects (200, 205, 220) in a plurality of physical storage devices (117, 118) housed in or directly attached to a plurality of host computers which host the multiple clients; and providing a file system interface for the object store to support multiple simultaneous access by the multiple clients to the objects (200, 205, 220) stored in the object store, including providing to the multiple clients an abstraction of the flat namespace used internally by the object store, the abstraction being a hierarchical namespace having a root directory and one or more subdirectories; creating a set of top-level file system objects which appear as the subdirectories of the root directory in the abstraction, wherein each top-level file system object represents a separate abstraction of a storage device having a separate namespace that is organized in accordance with a designated clustered file system, and wherein at least one said top-level file system object has a designated clustered file system designed to support simultaneous access by the clients up to a maximum limit; requesting, by the multiple clients, access to files using the designated clustered file system of respective top-level file system objects in the hierarchical namespace of the abstraction, and, in response, via the file system interface, using the flat namespace to manage and access relevant objects (200, 205, 220) internally within the object store. providing an object store which stores objects (200, 205, 220), wherein the object store internally manages and accesses the objects (200, 205, 220) using a flat namespace that maps unique identifiers to the stored objects (200, 205, 220), and wherein the object store stores the objects (200, 205, 220) in a plurality of physical storage devices (117, 118) housed in or directly attached to a plurality of host computers which host the multiple clients; and providing a file system interface for the object store to support multiple simultaneous access by the multiple clients to the objects (200, 205, 220) stored in the object store, including providing to the multiple clients an abstraction of the flat namespace used internally by the object store, the abstraction being a hierarchical namespace having a root directory and one or more subdirectories; creating a set of top-level file system objects which appear as the subdirectories of the root directory in the abstraction, wherein each top-level file system object represents a separate abstraction of a storage device having a separate namespace that is organized in accordance with a designated clustered file system, and wherein at least one said top-level file system object has a designated clustered file system designed to support simultaneous access by the clients up to a maximum limit; requesting, by the multiple clients, access to files using the designated clustered file system of respective top-level file system objects in the hierarchical namespace of the abstraction, and, in response, via the file system interface, using the flat namespace to manage and access relevant objects (200, 205, 220) internally within the object store.