• Journal of the Korea Society of Computer and Information
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• v.27 no.12
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• pp.1-8
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• 2022

As an efficient file system for SSD(Solid State Drive), F2FS is employed in the kernel of Linux operating system. F2FS applies various methods to improve performance by reflecting the characteristics of flash memory. One of them is improvement of the index structure that contains addresses of data blocks for each file. This paper presents a method for further improving performance by modifying the index structure of F2FS. F2FS manages all index blocks as logical numbers, and an address mapping table is used to find the physical block addresses of index blocks on flash memory. This paper shows performance improvement by applying logical numbers to the last level index blocks only. The count of mapping table search for a data block access is reduced to 1~2 from 1~4.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.85-91
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• 2019

In this paper, we propose a new logging and recovery scheme that is suited for the high-performance transaction processing system base on flash memory storage. The proposed scheme is designed by considering flash's I/O characteristic of asymmetric costs between page update/read operations. That is, we substitute the costly update operation with writing and real-time usage of snapshot log, which is for the page-level physical redo. From this, we can avoid costly rewriting of a dirty page when it is evicted form a buffering pool. while supporting efficient revery procedure. The proposed scheme would be not lucrative in the case of HDD-based system. However, the proposed scheme offers the performance advance sush as a reduced number of updates and the fast system recovery time, in the case of flash storage such as SSD (solid state drive). Because the proposed scheme can easily be applied to existing systems by saving our snapshot records and ordinary log records together, our scheme can be used for improving the performance of upcoming SSD-based database systems through a tiny modification to existing REDO algorithms.

• Journal of Digital Contents Society
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• v.12 no.2
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• pp.141-150
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• 2011

Recently the Solid State Drive (SSD) is widely used for storage system of various mobile devices. In this case, existing buffer replacement algorithms based on the hard disk do not consider characteristics of flash memory, so it caused performance degradation of the system. This paper proposes a novel buffer replacement policy called ABM (Asymmetric Buffer Management) policy. ABM policy separates read and write buffer space and applies different replacement unit and replacement algorithm for each buffer. In addition, write buffer delay scheme and dynamic size adaptation algorithm is applied for better performance. ABM outperforms other replacement policies, especially ABM-LRU-CLC shows 32% better performance than normal LRU policy.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.288-289
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• 2012

최근 데이터 저장을 위한 고속 입출력에서 병목현상을 해결하기 위해 다양한 SSD(Solid State Drive) 관련 연구가 많이 수행되고 있다. 대표적인 것으로 비휘발성 메모리인 플래시와 차세대 반도체 메모리인 SCM(Storage Class Memory) SSD가 있고, 휘발성 메모리인 DRAM기반의 SSD가 있다. 플래시 또는 SCM 메모리기반 저장장치는 하드 디스크기반 저장장치에 비해 읽기 속도가 빠르며, 내구성이 강하다는 장점으로 새로운 저장장치 시스템의 저장매체로 부각되고 있으나, 단위 저장 공간 당 높은 가격으로 인해 저장장치 시스템에 적용하기 에는 많은 문제점이 있다. 최근에는 이러한 문제를 해결하기 위해 고용량의 하드디스크와 SSD를 RAID 또는 단일 저장장치 매체로 구성하는 하이브리드 저장장치에 관한 연구와 제품이 출시되고 있다. 본 논문에서는 이러한 하이브리드 저장 매체 어레이를 저장장치 시스템으로 구성하기 위한 볼륨구성과 해당 서버에 볼륨 제공 서비스를 수행하기 위한 하이브리드 저장장치 시스템 설계 방법에 대해 설명한다.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.349-351
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• 2012

낸드 플래시 메모리에서 가비지 콜렉션은 블록의 유효한 데이터들을 새로운 블록으로 옮기고 오래된 블록을 지우는 과정이다. 가비지 콜렉션에 의해 옮겨지는 페이지들은 작업의 양과 형태에 따라 오랫동안 유효한 페이지로 존재하기도 하고 그렇지 않은 경우도 있다. 본 논문에서는 반도체 디스크(Solid State Drive, 이하 SSD)에서 가비지 콜렉션이 비효율적으로 일어나는 경우를 정의하고 비효율적 가비지 콜렉션 과정으로 인한 비용을 줄이는 캐시 방출 기법을 소개한다. 이 기법을 시뮬레이션 해본 결과 작업 형태가 순차적일 때 LRU 캐시 알고리즘과 같이 사용되면 가비지 콜렉션에 의해 옮겨지는 페이지를 12%, 전체 쓰기 연산 횟수를 9%까지 줄일 수 있었고 블록 단위 LRU 알고리즘과 사용했을 때도 보다 좋은 성능을 보였다.

• JSTS:Journal of Semiconductor Technology and Science
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• v.17 no.1
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• pp.15-22
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• 2017

Although there are many efficient techniques to minimize the speed gap between processor and the memory, it remains a bottleneck for various commercial implementations. Since secondary memory technologies are much slower than main memory, it is challenging to match memory speed to the processor. Usually, hard disk drives include semiconductor caches to improve their performance. A hit in the disk cache eliminates the mechanical seek time and rotational latency. To further improve performance a divided disk cache, subdivided between metadata and data, has been proposed previously. We propose a new algorithm to apply the SSD that is flash memory-based solid state drive by applying FTL. First, this paper evaluates the performance of such a disk cache via simulations using DiskSim. Then, we perform an experiment to evaluate the performance of the proposed algorithm.

• International Journal of Contents
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• v.5 no.4
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• pp.75-80
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• 2009

Recently high-speed memory array based on RAM, which is a type of solid-state drive (SSD), has been introduced to handle the input/output (I/O) bottleneck. But there are only a few performance studies on RAM based SSD storage with regard to diverse workloads. In this paper, we focus on the file system for RAM based memory array based NGS (Next Generation Storage) system which is running on Linux operating system. Then we perform benchmark tests on practical file systems including Ext3, ReiserFS, XFS. The result shows XFS significantly outperforms other file systems in tests that represent the storage and data requests typically made by enterprise applications in many aspects. The experiment is used to design the dedicated file system for NGS system. The results presented here can help enterprises improve their performance significantly.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.1118-1120
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• 2012

컴퓨터 메모리의 용량이 커지고 기술이 발전하며 메모리와 저장장치의 데이터 처리속도 차이는 나날이 커지고 있다. 이를 보완하고자 데이터 처리를 가급적 메모리에서 해결하여 처리속도를 높이고자 하는 연구가 많이 있다. 그 중 MapReduce에 대한 연구는 현재 주목이 되고 있는 분야이다. MapReduce는 빅데이터를 클러스터 환경에서 처리하기에 대중적인 프로그래밍 모델이다. 본 논문은 MapReduce 기반의 Hadoop을 SSD를 적용하여 실행속도를 증진시키려 한다. 전통적인 MapReduce 모델은 데이터를 정렬하는데에 I/O가 크게 발생하는데, MapRedce가 사용하는 병합정렬의 I/O 병목현상을 개선하고자 SSD를 사용하였다.

• Journal of the Korea Society of Computer and Information
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• v.24 no.9
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• pp.1-8
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• 2019

In this paper, we propose a performance isolation of shared space for virtualized SSD based storage systems, to solve the weakness in a VSSD framework. The proposed scheme adopts a CFQ scheduler and a shared space-based FTL for the fairness and the performance isolation for multiple users on virtualized SSD based storage systems. Using the CFQ scheduler, we ensure SLOs for the storage systems such as a service time, a allocated space, and a IO latency for users on the virtualized storage systems. In addition, to improve a throughput and reduce a computational latency for garbage collection, a shared space-based FTL is adopted to maintain the information of SLOs for users and it manages shared spaces among the users. In our experiments, the proposal improved the throughput of garbage collection by 7.11%, on average, and reduced the computational latency for garbage collection by 9.63% on average, compared to the previous work.

• KIPS Transactions on Computer and Communication Systems
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• v.4 no.9
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• pp.307-314
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• 2015

Recently, market trends of auxiliary storage device HDD and SSD are interchangeable. In the future, the SSD is expected to be used more popular than HDD as an auxiliary storage device. The TRIM command technique has been proposed and used effectively due to the development of the SSD. The TRIM command techniques can be used to solve the problem of Freezing SSD that operating system cooperates with the SSD. The TRIM command techniques are performed in the idle time of the internal SSD that are actually deleted when a user deletes the data. However, in the point of view of computer forensics, the digital crime is increasing year by year due to lack of data recovery. Thus, this rate of arrest is insufficient. In this paper, I propose a solution that selectively manages data to delete based on advantage of the stability and the write speed of the TRIM command. Through experiments, It is verified by measuring the performance of the traditional method and selected method.