HPSS User Interfaces

• File Transfer Protocol (FTP). HPSS provides an industry-standard FTP user interface. Because standard FTP is a serial interface, data sent to a user is received serially. This does not mean that the data within HPSS is not stored and retrieved in parallel; it simply means that the FTP Daemon within HPSS must consolidate its internal parallel transfers into a serial data transfer to the user. HPSS FTP performance in many cases will be limited not by the speed of a single storage device, as in most other storage systems, but by the speed of the data path between the HPSS FTP Daemon and the user's FTP client.

• Parallel FTP (PFTP). The PFTP supports standard FTP commands plus ext ensions and is built to optimize performance for storing and retrieving files from HPSS by allowing data to be transferred in parallel across the network media. The parallel client interfaces have a syntax similar to FTP but with some extensions to allow the user to transfer data to and from HPSS across parallel communication interfaces established between the FTP client and the HPSS Movers. This provides the potential for using multiple client nodes as well as multiple server nodes. The FTP client communicates directly with HPSS Movers to transfer data at rates limited only by the underlying communications hardware and software.

• Client Application Program Interface (Client API). The Client API is an HPSS-specific programming interface that mirrors the POSIX.1 specification where possible to provide ease of use to POSIX application programmers. Additional APIs are also provided to allow the programmer to take advantage of the specific features provided by HPSS (e.g., storage/access hints passed on file creation and parallel data transfers). The Client API is a programming level interface. It supports file open/create and close operations; file data and attribute access operations; file name operations; directory creation, deletion, and access operations; and working directory operations. HPSS users interested in taking advantage of parallel I/O capabilities in HPSS can add Client API calls to their applications to utilize parallel I/O.

• Virtual File System (VFS). The VFS server provides a native POSIX file system interface to access HPSS name space objects and bitfile data. A user can mount an HPSS directory and access it as if it were a locally mounted file system, using standard POSIX. Common commands include cp, mv, chmod and programmatic interface common usage include open, read, write.

• Parallel Input/Output API(PIO).  PIO provides a layer of abstraction to simplify the programming interface to the high performance and parallel readlist and writelist Client API calls.