• Journal of KIISE:Computing Practices and Letters
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• v.15 no.9
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• pp.685-689
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• 2009

Flash memory has several features such as low~power consumption and fast access so that there has been various research on using flash memory as new storage. Especially the Solid State Disk which is composed of flash memory chips has recently replaced the hard disk. At present, SSD adopts the multi-channel and multi-way architecture to exploit advantages of parallel access. In this architecture, data are written on SSD in a unit of a superblock which is composed of multiple blocks in which some blocks are put together. This paper proposes two schemes of selecting, segmenting and re-composing victim superblocks to optimize concurrent processing when a buffer flush occurs. The experimental results show that 35% of superblock- based write operations is reduced by selecting victims and additional 9% by composition of superblock.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.108-110
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• 1999

컴퓨터 하드웨어의 발달로 고속 네트워킹과 대용량 저장 장치가 가능해지면서 기존의 단순 계산 데이터가 아닌 멀티미디어 데이터를 조작하는 기술이 필요로 하게 되었다. 이 기술을 이용하는 대표적인 것이 VoD 서버 처리 기술이다. 기존 VoD 서버에서는 데이터의 분산 및 버퍼 구조 또는 병렬 I/O를 통하여 해결하려는 노력이 있어 왔다. 본 논문에서는 서버의 성능을 극대화시켰다. 디스크 저장 매체와 서버의 수를 증가시켜 시험하므로써 이 구조가 확장성 있음을 보였다.

• Proceedings of the Korean Information Science Society Conference
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• 2001.04a
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• pp.223-225
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• 2001

본 논문은 분산 환경에서 결함 허용성 있는 VoD서비스를 위한 결함 처리 방법을 제안하고 성능을 측정하였다. 디스크 결함, 서버 결함, 시스템 결함에 따른 결함 체크와 처리 방법을 제시하였다. 사용자에게 신뢰성과 실시간성을 보장하기 위한 서버 스위칭 방법을 제안하였다. 서버 스위칭 방법은 결함이 발생하지 않은 서버들의 여유 로드율에 따라 달라진다. 서버 스위칭이 일어나는 동안 클라이언트의 버퍼에 적정량의 데이터를 유지하기 위한 흐름제어 기법도 제시하였다. 본 논문에서 제안하는 방법을 통해 결함일 발생함에도 불구하고 클라이언트는 서비스의 중단 없이 VoD 서비스르 제공 받을 수 있다.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.5
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• pp.529-539
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• 2000

This paper proposes a prefetch-based disk buffer management algorithm, which we call W2R (Veighingjwaiting Room). Instead of using elaborate prefetching schemes to decide which blockto prefetch and when, we simply follow the LRU-OBL (One Block Lookahead) approach and prefetchthe logical next block along with the block that is being referenced. The basic difference is that theW2R algorithm logically partitions the buffer into two rooms, namely, the Weighing Room and theWaiting Room. The referenced, hence fetched block is placed in the Weighing Room, while theprefetched logical next block is placed in the Waiting Room. By so doing, we alleviate some inherentdeficiencies of blindly prefetching the logical next block of a referenced block. Specifically, a prefetchedblock that is never used may replace a possibly valuable block and a prefetched block, thoughreferenced in the future, may replace a block that is used earlier than itself. We show through tracedriven simulation that for the workloads and the environments considered the W2R algorithm improvesthe hit rate by a maximum of 23.19 percentage points compared to the 2Q algorithm and a maximumof 10,25 percentage feints compared to the LRU-OBL algorithm.

• Journal of Korea Society of Industrial Information Systems
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• v.15 no.2
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• pp.31-39
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• 2010

VoD(Video-on-Demand) servers have to provide timely processing guarantees for continuous media and reduce the storage and bandwidth requirements for continuous media. The compression techniques make the bit rates of compressed video data significantly variable from frame to frame. A VoD system should be able to provide the client with interactive operations such as fast forward and fast rewind in addition to normal playback of movie. However, interactive operations require additional resources such as storage space, disk bandwidth, memory and network bandwidth. In a stored video application such as VoD system, it is possible that a priori disk access patterns can be used to reserve the system resources in advance. In addition, clients of VoD server spend most of their time in playback mode and the period of time spent in interactive mode is relatively small. In this paper, I present the new buffer management scheme that provides efficient support for interactive operations in a VoD server using variable bit rate continuous media. Simulation results show that our strategy achieves 34% increase of the number of accepted clients over the LRU strategy.

• The KIPS Transactions:PartA
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• v.18A no.4
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• pp.135-142
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• 2011

This research is to design an effective buffer structure and its management for flash memory based high performance SSDs (Solid State Disks). Specifically conventional SSDs tend to show asymmetrical performance in read and /write operations, in addition to a limited number of erase operations. To minimize the number of erase operations and write latency, the degree of interleaving levels over multiple flash memory chips should be maximized. Thus, to increase the interleaving effect, an effective buffer structure is proposed for the SSD with a hybrid address mapping scheme and super-block management. The proposed buffer operation is designed to provide performance improvement and enhanced flash memory life cycle. Also its management is based on a new selection scheme to determine random and sequential accesses, depending on execution characteristics, and a method to enhance the size of sequential access unit by aggressive merging. Experiments show that a newly developed mapping table under the MBA is more efficient than the basic simple management in terms of maintenance and performance. The overall performance is increased by around 35% in comparison with the basic simple management.

• Journal of Korea Multimedia Society
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• v.10 no.11
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• pp.1384-1397
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• 2007

This paper proposes fast storage techniques for hybrid query of data streams. DSMS(Data Stream Management System) have been researched for processing data streams that have busting income. To process hybrid query that retrieve both current incoming data streams and past data streams data streams have to be stored into disk. But due to fast input speed of data stream and memory and disk space limitation, the main research is not about querying to stored data streams but about querying to current incoming data streams. Proposed techniques of this paper use circular buffer for maximizing memory utility and for make non blocking insertion possible. Data in a disk is compressed to maximize the number of data in the disk. Through experiences, proposed technique show that bursting insertion is stored fast.

• The Transactions of the Korea Information Processing Society
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• v.3 no.3
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• pp.617-630
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• 1996

In this paper, a shared-concurrent file system (S-CFS) is designed and implemented using conventional disks as disk arrays on a Workstation Cluster which can be used as a small-scale server. Since it is implemented on UNIX operating systems, S_CFS is not only portable and flexible but also efficient in resource usage because it does not require additional I/O nodes. The result of the research shows that on small-scale systems with enough disks, the performance of the concurrent file system on transaction processing applications is bounded by the bottleneck of CPUs computing powers while the performance of the concurrent file system on massive data I/Os is bounded by the time required to copy data between buffers. The concurrent file system,which has been implemented on a Workstation Cluster with 8 disks,shows a throughput of 388 tps in case of transaction processing applications and can provide the bandwidth of 15.8 Mbytes/sec in case of massive data processing applications. Moreover,the concurrent file system has been dsigned to enhance the throughput of applications requirring high performance I/O by controlling the paralleism of the concurrent file system on user's side.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.2
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• pp.242-260
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• 1999

실시간 데이터압축 기법은 저장 시스템의 용량과 저장 시스템간의 대역폭을 동시에 증가시킴으로써 프로세서-메모리, 메모리-디스크간의 성능 격차를 줄이기 위한 새로운 대안으로 연구되어 왔다. 하지만 압축데이타를 복원하는데 소요되는 시간은 압축 기법의 장점을 상쇄시킬 만큼 큰 오버헤드로 작용한다. 본 논문에서는 이러한 복원 오베헤드를 줄이기 위해 선택적 압축 기법과 복원 오버헤드 감춤 기법들을 적용한 선택적 압축 메모리 시스템을 제안하고 선택적으로 압축된 데이터를 효과적으로 접근하기 위한 캐쉬 구조와 메모리 운용방법을 제시한다. 제안된 선택적 압축 메모리 시스템의 성능은 분석적 모델과 트레이스 구동 방식의 실험을 통해 평가된다. 실험 결과에 따르면 선택적 압축 메모리 시스템의 성능은 데이터의 압축율과 응용 프로그램의 데이터 접근 유형에 따른 압축 블록의 참조율 및 복원 오버헤드를 줄이기 위해 장착된 복원 버퍼의 접근 성공률에 따라 좌우됨을 알 수있다. 복원 버퍼는 대부분의 벤치마크 프로그램들에 대해서 기존의 복원 오버헤드를 70% 이상 줄여 주며 이 경우 일반적인 메모리 시스템에 비해 최대 20%까지의 성능 향상을 보인다. 뿐만 아니라 선택적 압축 기법은 평균 47% 의 데이터 이동시간의 감소와 10%의 온 칩 캐쉬 접근 실패 횟수의 감소 효과를 제공한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.11a
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• pp.389-392
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• 2008

유비쿼터스 환경에서 센서 데이터는 빠르고 연속적인 데이터 스트림 형태로 전송된다. 이러한 개별적인 데이터 스트림 정보를 연관되어 처리하기 위해 조인 연산이 필요하다. LWO, SWF 와 같은 기존 기법들은 Nested Loop Join 을 이용해 데이터 스트림 환경에서 조인 알고리즘을 제시하였다. 하지만 Nested Loop Join 을 사용하기 때문에 슬라이딩 윈도우의 크기에 따라 처리 속도가 영향을 많이 받고 XJoin 은 디스크 I/O 추가 비용이 필요하다. 제안 기법은 환형 큐 버퍼 기반의 해시 색인을 이용한 조인 기법은 환형 큐를 이용하여 데이터의 삽입, 삭제를 관리하고 해시 색인을 이용해 조인 연산을 처리 하여 제안 기법은 기존의 기법 보다 조인 연산을 보다 효율적으로 처리 할 수 있다.