• 정보저장시스템학회논문집
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• 제6권2호
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• pp.63-67
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• 2010

Holographic data storage system is one of next generation high density optical memories. Thereby storing multiple data pages using multiplexing method in one spot, we can achieve high store density and fast access time. However, for uniform writing, we must control exposure time properly by the change of writing material characteristics. Many studies have been investigated about exposure time scheduling. However, once it is decided, we cannot change the scheduled time. Therefore, it is hard to obtain uniform data intensity. In this study, we propose exposure time control method using additional red beam as the monitoring signal. Through reconstructed red beam intensity in real time, we can adjust exposure time by the writing condition change. We construct compensation method mathematically and verify the feasibility of proposed method through the experiments.

• 정보저장시스템학회논문집
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• 제6권2호
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• pp.52-56
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• 2010

In this paper, we investigate the polarization multiplexing for micro holographic storage. The proposed multiplexing method is performed by using crystal media that use photorefractive materials such as Fe-doped $LiNbO_3$. We discuss the feasibility of fast recording, high capacity and transfer rate for polarization multiplexing method. Finally, we experimentally verify the proposed method using polarization selectivity.

• 정보저장시스템학회논문집
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• 제3권4호
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• pp.167-172
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• 2007

The recently-developed off-line learning control approaches for the rejection of periodic disturbances utilize the specific property that the learning system tends to oscillate in steady state. Unfortunately, the prior works have not clarified how closely the learning system should approach the steady state to achieve the rejection of periodic disturbances to satisfactory level. In this paper, we address this issue extensively for the class of linear systems. We also attempt to remove the effect of other aperiodic disturbances on the rejection of the periodic disturbances effectively. In fact, the proposed learning control algorithm can provide very fast convergence performance in the presence of aperiodic disturbance. The effectiveness and practicality of our work is demonstrated through mathematical performance analysis as well as various simulation results.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2015년도 추계학술발표대회
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• pp.211-213
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• 2015

SSD 등과 같이 다양한 성능을 가진 저장 장치가 개발되고 안정화 됨에 따라 분산 파일 시스템에서 다양한 저장 장치를 활용하기 위한 연구가 많이 진행되고 있다. 특히, 바이오 응용에서 대용량 분석에서 높은 IOPS가 요구가 증대되고 있으며, 이를 해결하기 위해 분산 파일 시스템에서 SSD 장치 등을 활용하는 것이 필요해지고 있다. 하지만 단순히 SSD만 사용한다고 해서 분산 파일 시스템의 성능이 빨라지는 것은 아니다. 오히려, 비용 대비 성능 상의 이점이 없을 수 있다. 본 논문에서는 대표적인 바이오 응용을 활용해 SSD와 HDD 융합 시험을 통해 분산 파일 시스템에서 SSD 활용에 대한 효과를 살펴보았다.

• Journal of Information Processing Systems
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• 제15권1호
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• pp.55-66
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• 2019

Storage system often applies erasure codes to protect against disk failure and ensure system reliability and availability. Liberation code that is a type of coding scheme has been widely used in many storage systems because its encoding and modifying operations are efficient. However, it cannot effectively achieve fast recovery from single disk failure in storage systems, and has great influence on recovery performance as well as response time of client requests. To solve this problem, in this paper, we present HRSF, a Hybrid Recovery method for solving Single disk Failure. We present the optimal algorithm to accelerate failure recovery process. Theoretical analysis proves that our scheme consumes approximately 25% less amount of data read than the conventional method. In the evaluation, we perform extensive experiments by setting different number of disks and chunk sizes. The results show that HRSF outperforms conventional method in terms of the amount of data read and failure recovery time.

• International Journal of Computer Science & Network Security
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• 제22권6호
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• pp.181-186
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• 2022

Cloud computing is the latest approach that is developed for reducing the storage of space to store the data and helps the quick sharing of the data. An increase in the cloud computing users is observed that is also making the users be prone to hacker's attacks. To increase the efficiency of cloud storage encryption mechanisms are used. The encryption techniques that are discussed in this survey paper are searchable encryption, attribute-based, Identity-based encryption, homomorphic encryption, and cloud DES algorithms. There are several limitations and disadvantages of each of the given techniques and they are discussed in this survey paper. Techniques are found to be effective and they can increase the security of cloud storage systems.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권10호
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• pp.5039-5061
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• 2017

Cloud storage becomes a new trend that more and more users move their data to cloud storage servers (CSSs). To ensure the security of cloud storage, many cloud auditing schemes are proposed to check the integrity of users' cloud data. However, most of them are based on public key infrastructure, which leads to complex certificates management and verification. Besides, most existing auditing schemes are inefficient when user uploads a large amount of data or a third party auditor (TPA) performs auditing for multiple users' data on different CSSs. To overcome these problems, in this paper, we propose an efficient and secure auditing scheme based on identity-based cryptography. To relieve user's computation burden, we introduce a proxy, which is delegated to generate and upload homomorphic verifiable tags for user. We extend our auditing scheme to support auditing for dynamic data operations. We further extend it to support batch auditing in multiple users and multiple CSSs setting, which is practical and efficient in large scale cloud storage system. Extensive security analysis shows that our scheme is provably secure in random oracle model. Performance analysis demonstrates that our scheme is highly efficient, especially reducing the computation cost of proxy and TPA.

• 한국통신학회논문지
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• 제29권4B호
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• pp.403-410
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• 2004

일반적으로 교환 시스템은 프로세서 보드, 입출력처리 보드 및 데이터 저장 장치등 그 기능별로 다수의 서브시스템들로 구성되어 있다. 또한 신뢰성을 확보하기 위하여 모든 서브 보드들은 이중화로 되어 있다. 교환시스템에서 저장 장치에는 시스템에 관련된 정보나 과금 정보등과 같은 작업 관련 데이터를 저장하며 비 휘발성 메모리에 저장해야 한다. 일반적으로 비 휘발성 저장장치를 구현할 때는 플래시메모리(flash memory) 또는 배터리 백업 메모리(battery backup memory)를 사용한다. 그러나 메모리는 단위 용량당 가격이 높고 백업(backup) 하지 않은 데이터를 손실했을 때 복구할 수 없다. 본 논문에서는 마이크로 컨트롤러를 이용하여 단위 용량당 가격이 저렴하고, 대용량의 데이터를 저장함과 동시에 이중화를 만족시키는 on-board 형태의 소형 디스크 모듈을 설계 구현하였다. 본 논문에서 구현된 이중화 저장장치는 사용 중인 엑티브(active) 디스크에 결함이 생겨 사용할 수 없을 경우에 리빌딩(rebuilding)과정을 동해 스탠바이 모듈로부터 데이터를 복구하며, 리빌딩 중에도 호스트 시스템은 스탠바이 디스크모듈을 이용하여 지속적으로 서비스를 제공할 수 있도록 설계되었다. 본 연구에서 개발된 저장장치는 교환시스템에서 플래시 메모리와 같은 값비싼 저장 장치를 대체 할 수 있을 것으로 기대된다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권1호
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• pp.227-247
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• 2018

For intermittently connected wireless sensor networks deployed in hash environments, sensor nodes may fail due to internal or external reasons at any time. In the process of data collection and recovery, we need to speed up as much as possible so that all the sensory data can be restored by accessing as few survivors as possible. In this paper a novel redundant data storage algorithm based on minimum spanning tree and quasi-randomized matrix-QRNCDS is proposed. QRNCDS disseminates k source data packets to n sensor nodes in the network (n>k) according to the minimum spanning tree traversal mechanism. Every node stores only one encoded data packet in its storage which is the XOR result of the received source data packets in accordance with the quasi-randomized matrix theory. The algorithm adopts the minimum spanning tree traversal rule to reduce the complexity of the traversal message of the source packets. In order to solve the problem that some source packets cannot be restored if the random matrix is not full column rank, the semi-randomized network coding method is used in QRNCDS. Each source node only needs to store its own source data packet, and the storage nodes choose to receive or not. In the decoding phase, Gaussian Elimination and Belief Propagation are combined to improve the probability and efficiency of data decoding. As a result, part of the source data can be recovered in the case of semi-random matrix without full column rank. The simulation results show that QRNCDS has lower energy consumption, higher data collection efficiency, higher decoding efficiency, smaller data storage redundancy and larger network fault tolerance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권9호
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• pp.4063-4086
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• 2016

Cloud computing is a robust technology, which facilitate to resolve many parallel distributed computing issues in the modern Big Data environment. Hadoop is an ecosystem, which process large data-sets in distributed computing environment. The HDFS is a filesystem of Hadoop, which process data blocks to the cluster nodes. The data block placement has become a bottleneck to overall performance in a Hadoop cluster. The current placement policy assumes that, all Datanodes have equal computing capacity to process data blocks. This computing capacity includes availability of same storage media and same processing performances of a node. As a result, Hadoop cluster performance gets effected with unbalanced workloads, inefficient storage-tier, network traffic congestion and HDFS integrity issues. This paper proposes a storage-tier-aware Robust Data Placement (RDP) scheme, which systematically resolves unbalanced workloads, reduces network congestion to an optimal state, utilizes storage-tier in a useful manner and minimizes the HDFS integrity issues. The experimental results show that the proposed approach reduced unbalanced workload issue to 72%. Moreover, the presented approach resolve storage-tier compatibility problem to 81% by predicting storage for block jobs and improved overall data block placement by 78% through pre-calculated computing capacity allocations and execution of map files over respective Namenode and Datanodes.