Age Aware Pre-emptive Garbage Collection for SSD RAID

Flash-based storage systems offer high performance, robustness, and reliability for embedded applications; however the physical nature of flash memory means that there are limitations to its usage in high reliability applications. In previous work, we have developed RAID architectures and associated controller hardware that increase the reliability and lifespan of these storage systems. However, flash memory needs regular garbage collection and this presents two issues in a high reliability context. The first issue concerns response times as when a garbage collector is active, the flash memory cannot be used by the application layer. This non-determinism in terms of response is problematic in high reliability systems that require real-time guarantees. The second issue concerns lifespan of flash chips. If the garbage collector is allowed free rein over erase operations while garbage collecting, this affects management of the lifespan of each SSD in the array. In this paper we present an enhanced, dynamic, real-time garbage collection method for SSD RAID that does not ignore the strict age distribution management, while offering deterministic response times for access. Real-time efficiency is further improved by dynamically coordinating garbage collection across each device in the array. Our simulation results indicate that the dynamic garbage collection technique maintains the age distribution at a level that does not affect reliability of individual devices. This is evidences using various synthetic and realistic traces dominated by random I/O loads

Winona Daily News

https://openriver.winona.edu/winonadailynews/1930/thumbnail.jp

Political economy of crisis, mining and accumulation in Zimbabwe : evidence from the Chegutu Mhondoro Area.

Ph.D. University of KwaZulu-Natal, Durban 2013.This thesis has its foundations in a 2007 master’s research on the political economy of “illegal” gold panning in central Zimbabwe. A book chapter (Moore and Mawowa, 2010) and a journal article (Mawowa, 2013) have since resulted from that work. The former work argues that illegal gold panning demonstrates a distinctive pattern of accumulation characterising post-2000 Zimbabwe. Four aspects of this pattern are identified namely, i) the link between coercion, chaos and disorder and wealth accumulation and political power retention, ii) the role of the state in this imbroglio, in particular, its pervasiveness and centrality, iii) that this pattern was shaped by and has remodelled the acquisitive instincts of Zimbabwe’s ruling elite and iv) a culture of ‘strategic contradictions’ within ruling elites abets this pattern of accumulation. This thesis does not move substantially from this premise. Instead, it recasts these observations within a much broader scope. While the Masters work was restricted to a very small area, this work looks at a much bigger area and in fact much further away from the area of MA research. While retaining the focus on political economy of mining, this work goes beyond illegal gold panning to encompass what is generally defined as artisanal and small scale (gold) mining (ASM) in the Chegutu Mhondoro area. Since this is an area where successful platinum mining is also taking place, it was opportune and indeed relevant to extend the question of political economy to this sector. This is not to suggest that there is a direct link (formal or informal) between ASM and platinum mining other than proximity. However, evidence presented in this thesis is telling in terms of the commonality between the two with regards to the four aspects of Zimbabwe’s post-2000 regime of accumulation

Commons people: managing music and culture in contemporary Yogyakarta

My research is about musicians, visual artists, music collectors, fans, curators and cultural activists, participating in the popular discourse of music through relevant music activities. It narrates these people, with some of their music-based plans and initiatives. It also narrates the implementation of the plans and initiatives takes place in Yogyakarta, Indonesia. It takes place in an urban media infrastructure setting. I employ self-organizing, collectivism, and institutionalization of cultural production as useful concepts to define the alternative milieu. It is the milieu which shapes the production of tools and ways of organizing a series of action on managing music, culture, and life. Music, which also serves as a commons, emerges as a horizon of possibilities, or a means, to be managed and maintained for different purposes. I propose sustainability as a shared imagination of what doing music means. The articulation of such imagination informs the structure of the dissertation. The structure articulates the questions brought about by managing commons; they are the questions about a sense of security, sustainability, and documentation. It provides insights into what aspects that the people need to work on when they think about music.Global Challenges (FSW

Computational Methods in Multi-Messenger Astrophysics using Gravitational Waves and High Energy Neutrinos

This dissertation seeks to describe advancements made in computational methods for multi-messenger astrophysics (MMA) using gravitational waves GW and neutrinos during Advanced LIGO (aLIGO)’s first through third observing runs (O1-O3) and, looking forward, to describe novel computational techniques suited to the challenges of both the burgeoning MMA field and high-performance computing as a whole. The first two chapters provide an overview of MMA as it pertains to gravitational wave/high energy neutrino (GWHEN) searches, including a summary of expected astrophysical sources as well as GW, neutrino, and gamma-ray detectors used in their detection. These are followed in the third chapter by an in-depth discussion of LIGO’s timing system, particularly the diagnostic subsystem, describing both its role in MMA searches and the author’s contributions to the system itself. The fourth chapter provides a detailed description of the Low-Latency Algorithm for Multi-messenger Astrophysics (LLAMA), the GWHEN pipeline developed by the author and used in O2 and O3. Relevant past multi-messenger searches are described first, followed by the O2 and O3 analysis methods, the pipeline’s performance, scientific results, and finally, an in-depth account of the library’s structure and functionality. In particular, the author’s high-performance multi-order coordinates (MOC) HEALPix image analysis library, HPMOC, is described. HPMOC increases performance of HEALPix image manipulations by several orders of magnitude vs. naive single-resolution approaches while presenting a simple high-level interface and should prove useful for diverse future MMA searches. The performance improvements it provides for LLAMA are also covered. The final chapter of this dissertation builds on the approaches taken in developing HPMOC, presenting several novel methods for efficiently storing and analyzing large data sets, with applications to MMA and other data-intensive fields. A family of depth-first multi-resolution ordering of HEALPix images — DEPTH9, DEPTH19, and DEPTH40 — is defined, along with algorithms and use cases where it can improve on current approaches, including high-speed streaming calculations suitable for serverless compute or FPGAs. For performance-constrained analyses on HEALPix data (e.g. image analysis in multi-messenger search pipelines) using SIMD processors, breadth-first data structures can provide short-circuiting calculations in a data-parallel way on compressed data; a simple compression method is described with application to further improving LLAMA performance. A new storage scheme and associated algorithms for efficiently compressing and contracting tensors of varying sparsity is presented; these demuxed tensors (D-Tensors) have equivalent asymptotic time and space complexity to optimal representations of both dense and sparse matrices, and could be used as a universal drop-in replacement to reduce code complexity and developer effort while improving performance of existing non-optimized numerical code. Finally, the big bucket hash table (B-Table), a novel type of hash table making guarantees on data layout (vs. load factor), is described, along with optimizations it allows for (like hardware acceleration, online rebuilds, and hard realtime applications) that are not possible with existing hash table approaches. These innovations are presented in the hope that some will prove useful for improving future MMA searches and other data-intensive applications