SPA: On-Line Availability Upgrades for Parity-based RAIDs through Supplementary Parity Augmentations

In this paper, we propose a simple but powerful on-line availability upgrade mechanism, Supplementary Parity Augmentations (SPA), to address the availability issue for parity-based RAID systems. The basic idea of SPA is to store and update the supplementary parity units on one or a few newly augmented spare disks for on-line RAID systems in the operational mode, thus achieving the goals of improving the reconstruction performance while tole-rating multiple disk failures and latent sector errors simultaneously. By applying the exclusive OR operations appropriately among supplementary parity, full parity and data units, SPA can reconstruct the data on the failed disks with a fraction of the original overhead that is proportional to the supplementary parity coverage, thus significantly reducing the overhead of data regeneration and decreasing recovery time in parity-based RAID systems. In particular, SPA has two supplementary-parity coverage orientations, SPA Vertical and SPA Diagonal, which cater to user’s different availability needs. The former, which calculates the supplementary parity of a fixed subset of the disks, can tolerate more disk failures and sector errors; whereas, the latter shifts the coverage of supplementary parity by one disk for each stripe to balance the workload and thus maximize the performance of reconstruction during recovery. The SPA with a single supplementary-parity disk can be viewed as a variant of but significantly different from the RAID5+0 architecture in that the former can easily and dynamically upgrade a RAID5 system to a RAID5+0-like system without any change to the data layout of the RAID5 system. Our extensive trace-driven simulation study shows that both SPA orientations can significantly improve the reconstruction performance of the RAID5 system while SPA Diagonal significantly improves the reconstruction performance of RAID5+0, at an acceptable performance overhead imposed in the operational mode. Moreover, our reliability analytical modeling and Sequential Monte-Carlo simulation demonstrate that both SPA orientations consistently more than double the MTTDL of the RAID5 system and improve the reliability of the RAID5+0 system noticeably

FAST: a scintillating tracker for antiproton cross section measurements

A scintillating fiber tracker (FAST, Fiber Antiproton Scintillating Tracker) has been developed in the framework of the ASACUSA collaboration to perform a low energy antiproton cross section measurement at the Antiproton Decelerator at CERN; this PhD Thesis will discuss the design, the development, the commissioning of the FAST detector and the preliminary results of the data taking held in July 2007. Chap. 1 is a review of the topical results in Antiproton Physics during the last 50 years. Chap. 2 focuses on detectors; since the detector chosen for our experiment is a scintillating fiber tracker, the most advanced fiber detection systems are reviewed. Chap. 3 describes the detector, a 2500 channel scintillating fiber tracker readout by 42 multianode photomultipliers a custom electronics. The design has been validated with montecarlo simulations and with dedicated beam tests on prototypes. The tracker has been tested with cosmic rays to characterize the efficiency, the time resolution and the spatial resolution. Chap. 4 describes the commissioning phase and reports the results of the data collected on the Antiproton Decelerator. In the last Chap. 3 applications of the system developed for FAST in different physics fields are shown. The electronics has been used in Medical Physics, allowing a ToF neutron detection in a radiotherapic environment, in imaging applications, connected to a GEM pad detector and as a beam profile monitor with high rate capabilities at the CERN SPS H8 beam line

1917-04-26 Paintsville Herald

Paintsville Herald published on April 26, 1917

Dependence-driven techniques in system design

Burstiness in workloads is often found in multi-tier architectures, storage systems, and communication networks. This feature is extremely important in system design because it can significantly degrade system performance and availability. This dissertation focuses on how to use knowledge of burstiness to develop new techniques and tools for performance prediction, scheduling, and resource allocation under bursty workload conditions.;For multi-tier enterprise systems, burstiness in the service times is catastrophic for performance. Via detailed experimentation, we identify the cause of performance degradation on the persistent bottleneck switch among various servers. This results in an unstable behavior that cannot be captured by existing capacity planning models. In this dissertation, beyond identifying the cause and effects of bottleneck switch in multi-tier systems, we also propose modifications to the classic TPC-W benchmark to emulate bursty arrivals in multi-tier systems.;This dissertation also demonstrates how burstiness can be used to improve system performance. Two dependence-driven scheduling policies, SWAP and ALoC, are developed. These general scheduling policies counteract burstiness in workloads and maintain high availability by delaying selected requests that contribute to burstiness. Extensive experiments show that both SWAP and ALoC achieve good estimates of service times based on the knowledge of burstiness in the service process. as a result, SWAP successfully approximates the shortest job first (SJF) scheduling without requiring a priori information of job service times. ALoC adaptively controls system load by infinitely delaying only a small fraction of the incoming requests.;The knowledge of burstiness can also be used to forecast the length of idle intervals in storage systems. In practice, background activities are scheduled during system idle times. The scheduling of background jobs is crucial in terms of the performance degradation of foreground jobs and the utilization of idle times. In this dissertation, new background scheduling schemes are designed to determine when and for how long idle times can be used for serving background jobs, without violating predefined performance targets of foreground jobs. Extensive trace-driven simulation results illustrate that the proposed schemes are effective and robust in a wide range of system conditions. Furthermore, if there is burstiness within idle times, then maintenance features like disk scrubbing and intra-disk data redundancy can be successfully scheduled as background activities during idle times

The Owl, vol. 10, no. 1

Contents: Monks and monasticism, Golden dreams - A poem, The uses of obstacles, Villae Nostrae Laudes, A vaction ramble, The tail of the ape and the ant, The glorious mark - a story at second hand, Miss Burke - my curious companion, Editor\u27s table, Idle notes, List of college exchanges, Noted and quotedhttps://scholarcommons.scu.edu/owl/1055/thumbnail.jp