• KIPS Transactions on Computer and Communication Systems
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• v.7 no.11
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• pp.275-280
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• 2018

The choice of a suitable distributed file system is required for loading large data and high-speed processing through subsequent applications in a cloud environment. In this paper, we propose a write performance improvement method based on GlusterFS and evaluate the performance of MapRFS, CephFS and GlusterFS among existing distributed file systems in cloud environment. The write performance improvement method proposed in this paper enhances the response time by changing the synchronization level used by the synchronous replication method from disk to memory. Experimental results show that the distributed file system to which the proposed method is applied is superior to other distributed file systems in the case of sequential write, random write and random read.

• Journal of KIISE
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• v.42 no.8
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• pp.954-960
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• 2015

It is important to improve the performance of storage in the home cloud environment within the virtualized IoT gateway since the performance of applications deeply depends on storage. Though SSD caching is applied in order to improve the storage, it is only used for read-cache due to the limitations of SSD such as poor write performance and small write endurance. However, it is important to improve performance of the write operation in the home cloud server, in order to improve the end-user experience. This paper propose a novel SSD caching which considers write-data as well as read-data. We validate the enhancement in the performance of random-write by transforming it to the sequential patterns.

• Journal of KIISE
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• v.43 no.2
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• pp.177-185
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• 2016

In this paper, we propose a hybrid write buffer architecture comprised of DRAM and NVRAM on SSD and a write buffer algorithm for the hybrid write buffer architecture. Unlike other write buffer algorithms, the proposed algorithm considers read pages as well as write pages to improve the performance of storage devices because most actual workloads are read-write mixed workloads. Through effectively managing NVRAM pages, the proposed algorithm extends the endurance of SSD by reducing the number of erase operations on NAND flash memory. Our experimental results show that our algorithm improved the buffer hit ratio by up to 116.51% and reduced the number of erase operations of NAND flash memory by up to 56.66%.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.409-411
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• 2003

요즘 값싼 PC들을 빠른 네트웍으로 묶어 놓은 성능을 얻고자하는 클러스터 컴퓨팅에 대한 연구가 활발히 이루어지면서 CPU나 메모리. 네트웍보다 상대적으로 느린 디스크에서 데이터를 읽어 효율적으로 파일 서비스를 하는 분산 파일 시스템이 개발되었다. 기존 분산 파일 시스템 중 클러스터 컴퓨팅에서 많이 사용하는 Linux 운영 체제에서 병렬 I/O를 사용하여 사용자에게 빠른 파일 서비스를 제공하여 주는 PVFS가 개발되었다. 기존 PVFS에서는 캐쉬 시스템을 제공하고 있지 않기 때문에 읽기 성능을 향상시키기 위하여 PVFS를 위한 상호 협력 캐치를 설계하고 구현하였다. PVFS를 위한 상호 협력 캐쉬는 클라이언트의 파일 캐쉬를 공유하여 파일 요구를 처리하는 기법으로 읽기 성능은 크게 향상되었다. 하지만 쓰기의 경우에는 다른 클라이언트에서 가지고 있던 모든 데이터를 찾아 해제하는 부하가 있기 때문에 성능이 좋지 않다. 따라서 본 논문에서는 PVFS를 위한 상호 협력 캐쉬에서 쓰기 성능 향상 기법인 두 단계 프로토콜을 제시하고 구현한다. 그리고 두 단계 프로토콜을 기존 PVFS와 PVFS를 위한 상호 협력 캐쉬 시스템과 성능을 비교, 분석한다.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.2
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• pp.77-88
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• 2009

According to the size of NAND flash memory as the storage system of mobile device becomes large, the performance of address translation and life cycle management in FTL (Flash Translation Layer) to interact with file system becomes very important. In this paper, we propose the continuity counters, which represent the number of continuous physical blocks whose logical addresses are consecutive, to reduce the number of address translation. Furthermore we propose the prefetching method which preloads frequently accessed pages into main memory to enhance I/O performance of flash memory. Besides, we use the 2-bit write prediction and asynchronous writing method to predict addresses repeatedly referenced from host and prevent from writing overhead. The experiments show that the proposed method improves the I/O performance and extends the life cycle of flash memory. As a result, proposed CFTL (Clustered Flash Translation Layer)'s performance of address translation is faster 20% than conventional FTLs. Furthermore, CFTL is reduced about 50% writing time than that of conventional FTLs.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.3
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• pp.336-340
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• 2010

Flash storages are prevalent as portable storage in computing systems. When we consider the detachability of Flash storage devices, data integrity becomes an important issue. To assure extreme data integrity, file systems synchronously write all file data to storage accompanying hot write references. In this study, we concentrate on the effect of hot write references on Flash storage, and we consider the effect of absorbing the hot write references via nonvolatile write cache on the performance of the FTL schemes in Flash storage. In 80 doing, we quantify the performance of typical FTL schemes for workloads that contain hot write references through a wide range of experiments on a real system environment. Through the results, we conclude that the impact of the underlying FTL schemes on the performance of Flash storage is dramatically reduced by absorbing the hot write references via nonvolatile write cache.

• Journal of Advanced Navigation Technology
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• v.14 no.5
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• pp.752-759
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• 2010

In this paper, we propose differential-logging method to improve the performance of RMW(Read Modify Write) operations of DDR-SSD based software RAID. Small writes that are frequently occurred in enterprise applications are main factor to degrade the performance of RAID5. Once a block is updated in RAID5, the parity block of the block must be updated to maintain consistency of parity. Therefore, to process a small write request, we need to read its parity block stored in disk, read old data, perform XOR operation, and write updated data and parity block. Several methods for hard disk based software RAID are proposed to solve the small write problems in RAID 5. Ln this paper, we propose a differential-logging method which carefully considers the DDR-SSD to solve the small write problem in RAID 5. We show that our proposed method out performs the existing software RAID in LINUX through simulations.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.155-157
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• 2012

최근 클라우드 컴퓨팅의 핵심 기술로서 가상화 기술이 대두되고 있다. 가상화는 컴퓨터 자원의 물리적인 특징을 추상화하여 사용자에게는 논리적 자원을 제공하고 이를 통해 기술적 및 관리적 이점을 제공한다. Xen 가상화 환경에서 가상머신에 디스크 공간을 할당하는 한 가지 방식으로 하나의 하드디스크 파티션을 가상머신에 할당하는 방식이 있다. 위와 같은 환경에서는 같은 하드디스크에 존재하는 가상머신들임에도 불구하고 데이터에 접근하는 물리적 특성으로 인해 읽기/쓰기 성능 불균형이 발생하고, 가상머신의 수가 증가함에 따라 파티션 간의 최단 탐색거리 증가로 인해 동시적 읽기/쓰기의 성능이 저하되는 문제점이 발생한다. 본 논문은 이러한 문제점을 해결하기 위해 새로운 파티션 구조인 Onion 파티션 구조를 제안한다. Xen버전 4.1의 환경에서 Domain-0 커널버전 2.6.32를 수정하여 구현 및 실험을 하였다. 실험 결과, 각 가상머신의 독립적 읽기/쓰기 성능 편차가 기존대비 8%, 10%수준으로 개선되었으며, 가상머신들의 동시적 읽기/쓰기 성능은 기존대비 156.76%, 119.01%의 성능 향상을 보였다.

• Journal of Korea Multimedia Society
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• v.7 no.5
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• pp.633-639
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• 2004

The performance of optimistic concurrency control schemes which are generally used for Mobile computing is very sensitive to the transaction abort rate. Even if the abort probability can be reduced by back-shifting the timestamp from the time of requesting a commit, some transactions continuously perform unnecessary operations after the transactions accessed write-write conflicting data. In this paper, we propose an optimistic protocol that can abort the transactions during the execution phase by using the write notification approach. The proposed protocol enhances the performance of the optimistic concurrency control by reducing the unnecessary operations. In addition, we present a simulation study that compares our schemes with the timestamp based certification scheme. This study shows that our scheme outperforms the timestamp based certification scheme.

• Journal of the Korea Society of Computer and Information
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• v.25 no.3
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• pp.1-9
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• 2020

In this paper, we propose an efficient adaptive write scheme that improves the performance of write operation in MLC STT-MRAM caches. The key idea of the proposed scheme is to perform the write operation fast if the target MLC STT-MRAM cells contain a dead block. Even if the fast write operation on the MLC STT-MRAM evicts a cache block from the MLC STT-MRAM cells, its performance impact is low if the evicted block is a dead block which is not used in the future. Through experimental evaluation with a memory simulator, we show that the proposed adaptive write scheme improves the performance of the MLC STT-MRAM caches by 17% on average.