EVENODD: An Efficient Scheme for Tolerating Double Disk Failures in RAID Architectures

We present a novel method, that we call EVENODD, for tolerating up to two disk failures in RAID architectures. EVENODD employs the addition of only two redundant disks and consists of simple exclusive-OR computations. This redundant storage is optimal, in the sense that two failed disks cannot be retrieved with less than two redundant disks. A major advantage of EVENODD is that it only requires parity hardware, which is typically present in standard RAID-5 controllers. Hence, EVENODD can be implemented on standard RAID-5 controllers without any hardware changes. The most commonly used scheme that employes optimal redundant storage (i.e., two extra disks) is based on Reed-Solomon (RS) error-correcting codes. This scheme requires computation over finite fields and results in a more complex implementation. For example, we show that the complexity of implementing EVENODD in a disk array with 15 disks is about 50% of the one required when using the RS scheme. The new scheme is not limited to RAID architectures: it can be used in any system requiring large symbols and relatively short codes, for instance, in multitrack magnetic recording. To this end, we also present a decoding algorithm for one column (track) in error

Design and Analysis of Capacity Extendmle Disk Array System: The Diagonal Move Algorithm

With increased I/O performance and at least one disk failure tolerance, data redundant disk array as secondary storage system efficiently translate from a conventional computer storage system to be with better I/O rate, higher data transfer rate, and stronger reliability than traditional large single-disk systems. The increased I/O performance in measurement of I/O operating rate and data transfer rate are mostly gained from simultaneous data retrieval from several disks which are organized in parallel as shown in Figure 2-1. This parallel disks organization lets us have better I/O operating rate than the singular disk architecture, since it has several disk- I/O operations running concurrently. The I/O operating rate is defined as the number of I/O operations per second. And the simultaneous data access from disks lets us have better data transfer rate than any singular disk architecture, since we are retrieving data from more than one disk at the same time. The data transfer rate is defined as amount of data transferred through the bus or network per second such as bits per second (BPS). The disk data access time is the composition of seek time, rotation time, and data transfer time. Because data transfer speed over the bus or network electronically is much faster than the slow mechanical disk drives, accessing several disks in parallel can contribute to the bus or network having better utilization

Prefetching and Caching Techniques in File Systems for Mimd Multiprocessors

The increasing speed of the most powerful computers, especially multiprocessors, makes it difficult to provide sufficient I/O bandwidth to keep them running at full speed for the largest problems. Trends show that the difference in the speed of disk hardware and the speed of processors is increasing, with I/O severely limiting the performance of otherwise fast machines. This widening access-time gap is known as the “I/O bottleneck crisis.” One solution to the crisis, suggested by many researchers, is to use many disks in parallel to increase the overall bandwidth. \par This dissertation studies some of the file system issues needed to get high performance from parallel disk systems, since parallel hardware alone cannot guarantee good performance. The target systems are large MIMD multiprocessors used for scientific applications, with large files spread over multiple disks attached in parallel. The focus is on automatic caching and prefetching techniques. We show that caching and prefetching can transparently provide the power of parallel disk hardware to both sequential and parallel applications using a conventional file system interface. We also propose a new file system interface (compatible with the conventional interface) that could make it easier to use parallel disks effectively. \par Our methodology is a mixture of implementation and simulation, using a software testbed that we built to run on a BBN GP1000 multiprocessor. The testbed simulates the disks and fully implements the caching and prefetching policies. Using a synthetic workload as input, we use the testbed in an extensive set of experiments. The results show that prefetching and caching improved the performance of parallel file systems, often dramatically

Hochleistungs-Transaktionssysteme: Konzepte und Entwicklungen moderner Datenbankarchitekturen

Das Buch richtet sich an Informatiker in Studium, Lehre, Forschung und Entwicklung, die an neueren Entwicklungen im Bereich von Transaktions- und Datenbanksystemen interessiert sind. Es entspricht einer überarbeiteten Version meiner im Februar 1993 vom Fachbereich Informatik der Universität Kaiserslautern angenommenen Habilitationsschrift. Neben der Präsentation neuer Forschungsergebnisse erfolgen eine breite Einführung in die Thematik sowie überblicksartige Behandlung verschiedener Realisierungsansätze, wobei auf eine möglichst allgemeinverständliche Darstellung Wert gelegt wurde. Der Text wurde durchgehend mit Marginalien versehen, welche den Aufbau der Kapitel zusätzlich verdeutlichen und eine schnelle Lokalisierung bestimmter Inhalte unterstützen sollen