Youngjin Yu

Enhancing QoS and Energy Efficiency of Realtime Network Application on Smartphone Using Cloud Computing

This paper proposes a scheme to enhance energy efficiency and QoS of real time network applications on smart phone. The scheme reduces energy consumption and increases the successful interaction rate between the client at smart phone and the busy server of real time network application by deploying a surrogate of the client at smart phone in cloud computing environment. All interactions among the client at smart phone, the application server and the surrogate in the cloud are controlled by tokens. The proposed scheme considers security as well as energy waste in the cloud.

Trust Assurance of Data in Cloud Computing Environment

Cloud Computing Environment provides users with a blue print of IT Utopia with virtualization; unbounded computing power and data storage free from the cost and the responsibility of maintenance for the IT resources. But, there are several issues to be addressed for the Cloud Computing Environment to be realized as the blue print because users cannot control the IT resources provided by the Cloud Computing Environment but can only use them. One of the issues is how to secure and to trust data in the Cloud Computing Environment. In this paper, an efficient and practical trust assurance of data with provenance in Cloud Computing Environment.

Shedding Light in the Black-Box : Structural Modeling of Modern Disk Drives

The performance of computer systems depends on relatively slow disk I/O performance. In order to improve the disk I/O performance, it is required to reduce a mechanical delay induced by the disk I/O operations. Several approaches have been proposed for it. However, because hard-disk storage hides too much information to the outside world, it makes difficult to predict exact internal layout of disk storage. This paper introduces a technique which brings this black box to light empirically. The technique can be called a gray-box approach due to the use of some prior knowledge about disk drives. We propose a new algorithm that extract disk model parameters and build overall multi-dimensional disk structural model for several up-to-data IDE disk drives whose internals are known as a black-box. We validate the model accuracy through seek time analysis. We expect our modeling result can be applied to many researches optimizing disk I/O performance.

Request Bridging and Interleaving: Improving the Performance of Small Synchronous Updates under Seek-Optimizing Disk Subsystems

Write-through caching in modern disk drives enables the protection of data in the event of power failures as well as from certain disk errors when the write-back cache does not. Host system can achieve these benefits at the price of significant performance degradation, especially for small disk writes. We present new block-level techniques to address the performance problem of write-through caching disks. Our techniques are strongly motivated by some interesting results when the disk-level caching is turned off. By extending the conventional request merging, request bridging increases the request size and amortizes the inherent delays in the disk drive across more bytes of data. Like sector interleaving, request interleaving rearranges requests to prevent the disk head from missing the target sector position in close proximity, and thus reduces disk latency. We have evaluated our block-level approach using a variety of I/O workloads and shown that it increases disk I/O throughput by up to about 50%. For some real-world workloads, the disk performance is comparable or even superior to that of using the write-back disk cache. In practice, our simple yet effective solutions achieve better tradeoffs between data reliability and disk performance when applied to write-through caching disks.

Systematic approach of using power save mode for cloud data processing services

Energy efficiency is becoming a key issue for IT operators and data centres. To provide Power Save Mode (PSM) for data processing applications in such environments, power down method as a scaling down technique is an effective solution toward energy proportionality. The existing solutions for the PSM are inefficient in the overall energy management, taking the full replication approach. We propose an efficient replica redistribution algorithm, and our experimental results show that our system significantly reduces the network usage and the elapsed time. Our system leads to a slight increase in running time compared with the full replication approach.

DASCA: Data Aware Scaling Down to provide power proportionality for distributed data processing frameworks

Distributed systems have led to the adoption of cloud computing concepts among countless enterprises. A large number of companies have already benefited from delegating IT services to cloud service providers. At the same time, the interest on energy efficiency has dramatically increased. Energy efficiency in large distributed systems is a big concern for system engineers. In addition, the proliferation of distributed data processing frameworks such as MapReduce have led to a vast amount of research and practices. In this paper, we are particularly interested in providing energy proportionality for MapReduce. To provide energy proportionality, we propose Data Aware Scaling Down (DASCA), a scaling down framework for MapReduce. There are two problems we must address in order to support scaling down for MapReduce. The first is to choose a proper set of nodes to suspend, which we call candidate set. The second is to minimize the replica redistribution which occurs during the initiation of power save mode. To address these problems, we use the data awareness of the MapReduce framework. To address the first problem, we provide two greedy algorithms which exploit the data awareness of MapReduce. To address the second problem, we propose locality aware replica redistribution to efficiently redistribute the lost replicas while preserving the availability of replicas and performance of distributed processing.

Practical Fault-Tolerant Framework for eScience Infrastructure

Many areas of science currently use computing resources as a important part of their research, and many research groups adopt cluster architecture to use them efficiently and manage them easily. Therefore, faulttolerance becomes a very important property for the computing resources. However, fault-tolerant systems have not yet been widely adopted because they are either hard to deploy, hard to use, hard to manage, hard to maintain, or hard to justify. This paper proposes a practical fault-tolerant system for eScience infrastructures. Our system uses checkpoint/ restart mechanism for fault-tolerance, and provides a easy mechanism to integrate with Grid services widely used in eScience. Additionally, we run rigorous tests using scientific applications to verify that our system can be used in clusters. We also describe improvements made to our system to solve various problems that arose when deploying it on a cluster. The experimental results show that not only does our system conform to various types of running environment well, but that it can also be practically deployed in clusters.

SHIELD: a fault-tolerant MPI for an infiniband cluster

Todays high performance cluster computing technologies demand extreme robustness against unexpected failures to finish aggressively parallelized work in a given time constraint. Although there has been a steady effort in developing hardware and software tools to increase fault-resilience of cluster environments, a successful solution has yet to be delivered to commercial vendors. This paper presents SHIELD, a practical and easily-deployable fault-tolerant MPI and management system of MPI for an Infiniband cluster. SHIELD provides a novel framework that can be easily used in real cluster systems, and it has different design perspectives than those proposed by other fault-tolerant MPI. We show that SHIELD provides robust fault-resilience to fault-vulnerable cluster systems and that the design features of SHIELD are useful wherever fault-resilience is regarded as the matter of utmost importance.