• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.151-154
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• 2012

최근 차세대 저장장치로서 비휘발생 플래시 메모리 기반 저장장치의 사용이 층가하고 있다. 본 논문에서는 플래시 메모리 기반 저장장치의 특생인 삭제 연산의 문제점을 고려하는 새로운 버퍼 캐시 교체 기법을 연구하였다. 제안한 클린 블록 우선 (Clean Block First) 기법은 버퍼를 플래시 메모리의 삭제 블록의 리스트로 관리하고 클린 페이지를 가진 블록을 우선적으로 교체하여 플래시 메모리의 삭제 연산 횟수를 줄인다. 트레이스 기반의 시뮬레이션을 수행하여 교체를 위해 검색하는 클린 블록 개수의 변화에 대한 캐시 적중률과 삭제 연산 횟수를 분석하였다.

• Journal of KIISE:Computing Practices and Letters
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• v.10 no.2
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• pp.134-145
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• 2004

With rapid growth in the amount of data transferred on the Internet, traditional storage systems have reached the limits of their capacity and performance. SAN (Storage Area Network), which connects hosts to disk with the Fibre Channel switches, provides one of the powerful solutions to scale the data storage and servers. In this environment, the maintenance of data consistency among hosts is an important issue because multiple hosts share the files on disks attached to the SAN. To preserve data consistency, each host can execute the disk I/O whenever disk read and write operations are requested. However, frequent disk I/O requests cause the deterioration of the overall performance of a SAN cluster. In this paper, we introduce a SANtopia global buffer manager to improve the performance of a SAN cluster reducing the number of disk I/Os. We describe the design and algorithms of the SANtopia global buffer manager, which provides a buffer cache sharing mechanism among the hosts in the SAN cluster. Micro-benchmark results to measure the performance of block I/O operations show that the global buffer manager achieves speed-up by the factor of 1.8-12.8 compared with the existing method using disk I/O operations. Also, File system micro-benchmark results show that SANtopia file system with the global buffer manager improves performance by the factor of 1.06 in case of directories and 1.14 in case of files compared with the file system without a global buffer manager.

• Journal of KIISE:Databases
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• v.37 no.6
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• pp.308-314
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• 2010

As the price of flash memory continues to drop and the technology of flash SSD controller innovates, high performance flash SSDs with affordable prices flourish in the storage market. Nevertheless, it is hard to expect that flash SSDs will replace harddisks completely as database storage. Instead, the approach to use flash SSD as a cache for harddisks would be more practical, and, in fact, several hybrid storage architectures for flash memory and harddisk have been suggested in the literature. In this paper, we propose a new approach to use flash SSD as an extended buffer for main buffer in database systems, which stores the pages replaced out from main buffer and returns the pages which are re-referenced in the upper buffer layer, improving the system performance drastically. In contrast to the existing approaches to use flash SSD as a cache in the lower storage layer, our approach, which uses flash SSD as an extended buffer in the upper host, can provide fast random read speed for the warm pages which are being replaced out from the limited main buffer. In fact, for all the pages which are missing from the main buffer in a real TPC-C trace, the hit ratio in the extended buffer could be more than 60%, and this supports our conjecture that our simple extended buffer approach could be very effective as a cache. In terms of performance/price, our extended buffer architecture outperforms two other alternative approaches with the same cost, 1) large main buffer and 2) more harddisks.

• Journal of the Korea Society of Computer and Information
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• v.14 no.4
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• pp.9-17
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• 2009

In this paper, we propose a dynamic load distribution technique at the operating system level in mobile storage systems with a heterogeneous storage pair of a small form-factor and disk and a flash memory, which aims at saving energy consumption as well as enhancing I/O performance. Our proposed technique takes a combinatory approach of file placement and buffer cache management techniques to find how the load can be distributed in an energy and performance-aware way for a heterogeneous mobile storage air of a hard disk and a flash memory. We demonstrate that the proposed technique provides better experimental results with heterogeneous mobile storage devices compared with the existing techniques through extensive simulations.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.265-267
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• 2012

최근 들어, 하드웨어 플랫폼은 다수의 코어 아키텍처의 메모리 대역폭을 유지하기 위해 NUMA 구조로 설계되고 있다. 이러한 NUMA 시스템 구조에서 다른 노드의 메모리에 접근할 경우, 더 많은 시간과 비용이 소모된다. 따라서 이를 고려한 스케줄링 기법들이 가상화 혹은 가상화되지 않은 시스템 환경에서 연구되고 있다. 하지만, 아직까지 NUMA 시스템 가상화 환경에서 리모트 접근을 제거함과 동시에 이에 따른 오버헤드를 최소화하는 연구는 없었다. 따라서 본 논문에서는 이러한 환경에서 메모리 접근 지연을 줄이기 위한 VCPU 스케줄링 기법을 제안한다. 본 기법은 노드별 페이지 테이블 관리, LRU 기반 게스트 스케줄러, 캐시 오염 태스크 전용 버퍼 관리 기술을 이용한다. 다른 기법들과의 비교 및 분석 결과에서 알 수 있듯이, 본 기법을 적용할 경우 NUMA 시스템 노드 간 리모트 접근을 없애고, 이에 따른 오버헤드를 최소화하며, 주어진 하드웨어 캐시를 효율적으로 사용할 수 있다.

• Journal of the Korea Society of Computer and Information
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• v.15 no.11
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• pp.135-142
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• 2010

QoS in the proxy system are under heavy influence from interferences such as congestion, latency, and retransmission. Also, multi-level streaming services affects from temporal synchronization, which lead to degrade the service quality. This paper proposes a new segment-based buffer management mechanism which reduces performance degradation of streaming services and enhances throughput of streaming due to drawbacks of the proxy system. The proposed paper optimizes streaming services by: 1) Use of segment-based buffer management mechanism, 2) Minimization of overhead due to congestion and interference, and 3) Minimization of retransmission due to disconnection and delay. This paper utilizes fuzzy value $\mu$ and cost weight $\omega$ to process the result. The simulation result shows that the proposed mechanism has better performance in buffer cache control rate, average packet loss rate, and delay saving rate with stream relevance metric than the other existing methods of fixed segmentation method, pyramid segmentation method, and skyscraper segmentation method.

• Journal of the Korea Society for Simulation
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• v.12 no.2
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• pp.35-44
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• 2003

The effectiveness of buffer cache replacement algorithms is critical to the performance of I/O systems. In this paper, we propose the degree of inter-reference gap (DIG) based block replacement scheme that retains merits of the least recently used (LRU) such as simple implementation and good cache hit ratio (CHR) for general patterns of references, and improves CHR further. In the proposed scheme, cache blocks with low DIGs are distinguished from blocks with high DIGs and the replacement block is selected among high DIGs blocks as done in the low inter-reference recency set (LIRS) scheme. Thus, by having the effect of the partitioning the cache memory dynamically based on DIGs, CHR is improved. Trace-driven simulation is employed to verified the superiority of the DIG based scheme and shows that the performance improves up to about 175% compared to the LRU scheme and 3% compared to the LIRS scheme for the same traces.

• Proceedings of the Korean Society of Computer Information Conference
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• 2014.07a
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• pp.235-236
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• 2014

플래시 메모리 기술이 발전함에 따라 낸드 플래시 기반의 SSD가 상용화 되면서 I/O시간을 줄이기 위한 연구들이 진행되고 있다. 이에 본 논문에서는 기존의 메인 메모리와 저장장치 사이에 확장 버퍼 캐시로써 SSD를 사용하고 메인 메모리에서 방출 된 페이지들을 구분하여 같은 성향의 페이지들을 블록화 하는 모델을 제안한다. 이러한 모델을 통하여 블록 단위로 사용되는 SSD를 효율적으로 이용하여 읽기 및 쓰기 성능을 높이고 I/O에 해당하는 시간들을 줄임으로써 전체적인 성능 향상을 증명하였다.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.5
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• pp.412-421
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• 2009

Due to the physical characteristics of NAND flash memory, overwrite operations are not permitted at the same location, and therefore erase operations are required prior to rewriting. These extra operations cause performance degradation of NAND flash memory file system. Since it also has an upper limit to the number of erase operations for a specific location, frequent erases should reduce the lifetime of NAND flash memory. These problems can be resolved by delaying write operations in order to improve I/O performance: however, it will lower the cache hit ratio. This paper proposes a policy of page management using double cache for NAND flash memory file system. Double cache consists of Real cache and Ghost cache to analyze page reference patterns. This policy attempts to delay write operations in Ghost cache to maintain the hit ratio in Real cache. It can also improve write performance by reducing the search time for dirty pages, since Ghost cache consists of Dirty and Clean list. We find that the hit ratio and I/O performance of our policy are improved by 20.57% and 20.59% in average, respectively, when comparing them with the existing policies. The number of write operations is also reduced by 30.75% in average, compared with of the existing policies.

• Proceedings of the Korea Information Processing Society Conference
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• 2022.11a
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• pp.2-4
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• 2022

매니코어 CPU 시스템에서의 병렬 I/O 는 현재의 리눅스 시스템의 LRU 관리 방법의 한계로 확장성에 문제를 가지고 있다. 본 연구에서는 이 문제를 해결했던 하기 위한 개선된 FinerLRU 를 제안한다. LRU 락을 최대 코어 개수만큼 증가시키고 세분화된 Lock 관리를 통해 버퍼 캐시를 사용하는 파일 시스템의 병렬 I/O 성능을 향상시킨다. 리눅스 5.18.11 에 제안한 방법을 구현하였으며, 64 개의 물리적 코어와 256 개의 논리적 코어를 가지는 Intel Knights Landing 프로세서를 이용한 실험을 통해 두 배 가량의 성능 향상을 얻을 수 있음을 확인하였다.