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This article describes an implementation of MPI-IO using a new parallel file system, called Expand (Expandable Parallel File System), which is based on NFS servers. Expand combines multiple NFS servers to create a distributed partition where files are striped. Expand requires no changes to the NFS server and uses RPC operations to provide parallel access to the same file. Expand is also independent of the clients, because all operations are implemented using RPC and NFS protocols. Using this system, we can join heterogeneous servers (Linux, Solaris, Windows 2000, etc.) to provide a parallel and distributed partition. The article describes the design, implementation and evaluation of Expand with MPI-IO. This evaluation has been made in Linux clusters and compares Expand and PVFS.

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Parallelism in file systems is obtained by using several independent server nodes supporting one or more secondary storage devices. This approach increases the performance and scalability of the system, but a fault in one single node can stop the whole system. To avoid this problem, data must be stored using some kind of redundant technique, so any data stored in a faulty element can be recovered. Fault tolerance can be provided in I/O systems using replication or RAID based schemes. However, most of the current systems apply the same technique for all files in the system. 1 This paper describes the fault tolerance support provided by Expand, a parallel file system based on standard servers. Expand allows to define different fault-tolerant mechanisms at file level. The evaluation compare the performance of Expand with different configurations with PVFS using the FLASH-I/O benchmark.

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Functional requirements for information systems can be modeled through use cases. Furthermore, use case models have been successfully used in broader contexts than software engineering, as systems engineering. Even if small systems may be modeled as a set of use cases, when large systems requirements are modeled with a plain use case model several difficulties arise. Traditionally, the behavior of use cases has been modeled through textual specifications. In this paper we present an alternate approach based on interaction modeling. The behavior modeling has two variants (one for UML 1.x and one for UML 2.0). We also integrate our behavior modeling with standard use case relationships.

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