A method in a computer system , the method comprising: providing an object store which stores objects , wherein the object store internally manages and accesses the objects using a flat namespace that maps unique identifiers to the stored objects , and wherein the object store stores the objects in a plurality of physical storage devices 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 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 internally within the object store . providing an object store which stores objects , wherein the object store internally manages and accesses the objects using a flat namespace that maps unique identifiers to the stored objects , and wherein the object store stores the objects in a plurality of physical storage devices 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 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 internally within the object store . <EOS>