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ABSTRACT: One of the most common techniques to evaluate the performance of a computer I/O subsystem performance has been found on detailed simulation models including specific features of storage devices like disk geometry, zone splitting, caching, read-ahead buffers and request reordering. However, as soon as a new technological innovation is added, those models need to be reworked to include new devices making difficult to have general models up to date. Another alternative is modeling a storage device as a black-box probabilistic model, where the storage device itself, its interface and the interconnection mechanisms are modeled as a single stochastic process, defining the service time as a random variable with an unknown distribution. This approach allows generating disk service times needing less computational power by means of a variate generator included in a simulator. This approach allows to reach a greater scalability in the I/O subsystems performance evaluation by means of simulation. In this paper, we present a method for building a variate generator from service time experimental data. In order to build the variate generator, both real workloads and synthetic workloads may be used. The workload is used to feed the evaluated disk to obtain service time measurements. From experimental data we build a variate generator that fits the disk service times distribution. We also present a use case of our method, where we have obtained a relative error ranging from 0.45% to 1%.
Simulation Symposium, 2008. ANSS 2008. 41st Annual; 05/2008
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ABSTRACT: This paper presents a new probabilistic model which describes the way data blocks belonging to a certain file are distributed along the disk in general purpose systems. The distribution type is classified depending on the kind of file system, the file size and the disk occupancy ratio. The resulting algorithm will be used to simulate the access time to the data stored on a disk of an I/O node, where the position of data blocks determines the access time. In order to perform the modeling, some parameters have been estimated using some stress tests with different degrees of disk occupancy and file sizes on Ext2 and ReiserFS file systems.
Simulation Symposium, 2008. ANSS 2008. 41st Annual; 05/2008
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ABSTRACT: In this paper we present an implementation of a computer-based railway information system. This system requires a distributed infrastructure that should offer a high availability. The solution proposed is distributed into three kind of nodes: a node that implements the system interface for administering and monitoring using an ubiquitous Web application, a central computer that stores the data and serves as the union nexus and an embedded computer on each station for controlling the station elements (displays, megaphones, etc). The system can also make VoIP connections between the interface and the station. This paper describes the major issues faced during the designing of this railway information system that are related to achieve a high availability.
Database and Expert Systems Applications, 2005. Proceedings. Sixteenth International Workshop on; 09/2005
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ABSTRACT: This paper presents main experiences on designing and implementing a prototype for remote monitoring and management of unattended remote train stations information system. The prototype has several types of information sources, for example proprietary host terminal, streaming voice, encoded files, database information, etc., in remote places with different qualities (synchronous, periodic, etc.). In this paper we describe the major problems in this kind of system and how we have solved them
Industrial Informatics, 2004. INDIN '04. 2004 2nd IEEE International Conference on; 07/2004
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ABSTRACT: One important piece of system software for clusters is the parallel file system. All current parallel file systems and parallel I/O libraries for clusters do not use standard servers, thus it is very difficult to use these systems in heterogeneous environments. However why use proprietary or special-purpose servers on the server end of a parallel file system when you have most of the necessary functionality in NFS servers already? This paper describes the fault tolerance implemented in Expand (Expandable Parallel File System), a parallel file system based on NFS servers. Expand allows the transparent use of multiple NFS servers as a single file system, providing a single name space. The different NFS servers are combined to create a distributed partition where files are stripped. 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 protocol. Using this system, we can join heterogeneous servers (Linux, Solaris, Windows 2000, etc.) to provide a parallel and distributed partition. Fault tolerance is achieved using RAID techniques applied to parallel files. The paper describes the design of Expand and the evaluation of a prototype of Expand, using the MPI-IO interface. This evaluation has been made in Linux clusters and compares Expand with PVFS.
Parallel, Distributed and Network-Based Processing, 2003. Proceedings. Eleventh Euromicro Conference on; 03/2003
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ABSTRACT: The paper describes new techniques to increase the performance of collective communication operations in clusters. These techniqnes are based in multithreading operations and on-line data compression. The techniques proposed have been implemented in MiMPI, a thread-safe implementation of MPI. We have evaluated, and compared, the performance of MiMPI with other implementations of MPI available for clusters with Linux and Windows 2000. The benchmark used has been MPBench, a flexible and portable framework to allow benchmarking of MPI implementations.
Parallel Processing, International Conference on, 2001.; 10/2001
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ABSTRACT: During the last years, Internet video streaming has experiences a phenomenal growth. This is happening despite the notorious difficulties of transmitting data packets with a deadline over the Internet, due to variability in throughput, delays and losses. These problems arise significantly when using wireless networks where the available bandwidth is low and the losses are important due to its error prone transmission nature. In this paper we propose a fast-forwarding technique that is based on segmenting the movie on different files. Normal movie reproduction requires all the files, but fast-forwarding reproduction only requires one file. Those files can me merged by the client or by the server. The segmentation is frame based, grouping all the frames that can be independently decoded together. The resulting file can be showed with any existing player. This group of frames would be the ones to use in a fast-forward reproduction. Our techniques can also be useful in adaptive environments, like wireless networks, because there is no problem for the fast-forward file to use the same optimizations that exist for full movie files. This method also reduces the storage bandwidth and the storage size needed (there is no extra data for fast-forwarding). We also propose a video server architecture that takes advantage of this technique to achieve full interactive video reproduction. The evaluation results shown in this paper demonstrates that our technique enhances video fast-forwarding operations.
Computers and Communication, 2003. (ISCC 2003). Proceedings. Eighth IEEE International Symposium on;
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ABSTRACT: Nowadays, multimedia systems are evolving towards integrated storage platforms that meet the requirements of deterministic applications, multimedia systems, and traditional best-effort applications altogether These systems must incorporate a disk scheduling mechanism and a cache architecture that can handle the requirements of each kind of request while showing a good overall performance. In this paper a new interval caching strategy is proposed that includes several optimizations to the state of the art. This algorithm has been designed to become part of MUPIC (multipolicy integrated cache), a cache architecture designed to fit the requirements of an integrated storage system. This paper presents the mathematical enunciation that led us to deploy new interval caching strategies and an evaluation of the algorithm proposed using a simulation program that compares it with other algorithms described in the bibliography. As shown in the conclusions MUPIC behaves the same or better in all the situations while providing admission control.
Simulation Symposium, 2003. 36th Annual;
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ABSTRACT: In this paper a new multimedia caching strategy is proposed that includes several optimizations to the state of the art. This algorithm takes its roots from the interval caching algorithms but it evolves towards a more adaptive approaching that could obtain a better performance for variable bit-rate streams and serving media stored on multiple disks following different distributions. All of this without loosing competitiveness for constant bit-rate streams on a single disk. All this efforts are oriented towards the consecution of MUPIC (multi policy integrated cache), a cache architecture designed to fit the requirements of an integrated storage system that meet the requirements of deterministic applications, multimedia systems, and traditional best-effort applications altogether.
Automated Production of Cross Media Content for Multi-Channel Distribution, 2005. AXMEDIS 2005. First International Conference on;
