• Title, Summary, Keyword: FTL

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FlaSim: A FTL Emulator using Linux Kernel Modules (FlaSim: 리눅스 커널 모듈을 이용한 FTL 에뮬레이터)

  • Choe, Hwa-Young;Kim, Sang-Hyun;Lee, Seoung-Won;Park, Sang-Won
    • Journal of KIISE:Computing Practices and Letters
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    • v.15 no.11
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    • pp.836-840
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    • 2009
  • Many researchers have studied flash memory in order to replace hard disk storages. Many FTL algorithms have been proposed to overcome physical constraints of flash memory such as erase-before-write, wear leveling, and poor write performance. Therefore, these constraints should be considered for testing FTL algorithms and the performance evaluation of flash memory. As doing the experiments, we suffer from several problems with costs and settings in experimental configuration. When we, for example, replay the traces of Oracle to evaluate the I/O performance with flash memory, it is hard to extract exact traces of I/O operations in Oracle. Since there are only write operations in the log, it is impossible to gather read operations. In MySQL and SQLite, we can gather the read operations by changing I/O functions in the source codes. But it is not easy to search for the exact points about I/O and even if we can find out the points, we might get wrong results depending on how we modify source codes to get I/O traces. The FlaSim proposed in this paper removes the difficulties when we evaluate the performance of FTL algorithms and flash memory. Our Linux drivers emulate the flash memory as a hard disk. And we can easily obtain the usage statistics of flash memory such as the number of write, read, and erase operations. The FlaSim can be gracefully extended to support the additional modules implemented by novel algorithms and ideas. In this paper, we describe the structure of FTL emulator, development tools and operating methods. We expect this emulator to be helpful for many experiments and research with flash memory.

The Effect of Absorbing Hot Write References on FTLs for Flash Storage Supporting High Data Integrity (데이터 무결성을 보장하는 플래시 저장 장치에서 잦은 쓰기 참조 흡수가 플래시 변환 계층에 미치는 영향)

  • Shim, Myoung-Sub;Doh, In-Hwan;Moon, Young-Je;Lee, Hyo-J.;Choi, Jong-Moo;Lee, Dong-Hee;Noh, Sam-H.
    • 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.

Efficiently Managing the B-tree using Write Pattern Conversion on NAND Flash Memory (낸드 플래시 메모리 상에서 쓰기 패턴 변환을 통한 효율적인 B-트리 관리)

  • Park, Bong-Joo;Choi, Hae-Gi
    • Journal of KIISE:Computer Systems and Theory
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    • v.36 no.6
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    • pp.521-531
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    • 2009
  • Flash memory has physical characteristics different from hard disk where two costs of a read and write operations differ each other and an overwrite on flash memory is impossible to be done. In order to solve these restrictions with software, storage systems equipped with flash memory deploy FTL(Flash Translation Layer) software. Several FTL algorithms have been suggested so far and most of them prefer sequential write pattern to random write pattern. In this paper, we provide a new technique to efficiently store and maintain the B-tree index on flash memory. The operations like inserts, deletes, updates of keys for the B-tree generate random writes rather than sequential writes on flash memory, leading to inefficiency to the B-tree maintenance. In our technique, we convert random writes generated by the B-tree into sequential writes and then store them to the write-buffer on flash memory. If the buffer is full later, some sequential writes in the buffer will be issued to FTL. Our diverse experimental results show that our technique outperforms the existing ones with respect to the I/O cost of flash memory.

The Construction Work Completion of the Fuel Test Loop (핵연료 노내조사시험설비 설치공사 완료)

  • Park, Kook-Nam;Lee, Chung-Young;Chi, Dae-Young;Park, Su-Ki;Shim, Bong-Sik;Ahn, Sung-Ho;Kim, Hark-Rho;Lee, Jong-Min
    • Proceedings of the KSME Conference
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    • pp.291-295
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    • 2007
  • FTL(Fuel Test Loop) is a facility that confirms performance of nuclear fuel at a similar irradiation condition with that of nuclear power plant. FTL consists of In-Pile Test Section (IPS) and Out-Pile System (OPS). FTL construction work began on August, 2006 and ended on March, 2007. During Construction, ensuring the worker's safety was the top priority and installation of the FTL without hampering the integrity of the HANARO was the next one. Task Force Team was organized to do a construction systematically and the communication between members of the task force team was done through the CoP(community of Practice) notice board provided by the Institute. The installation works were done successfully overcoming the difficulties such as on the limited space, on the radiation hazard inside the reactor pool, and finally on the shortening of the shut down period of the HANARO. Without a sweet of the workers of the participating company of HEC(Hyundae Engineering Co, Ltd), HDEC(HyunDai Engineering & Construction Co. Ltd), equipment manufacturer, and the task force team, it is not possible to install the FTL facility within the planned shutdown period. The Commissioning of the FTL is on due to check the function and the performance of the equipment and the overall system as well. The FTL shall start operation with high burn up test fuels in early 2008 if the commissioning and licensing progress on schedule.

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EAST: An Efficient and Advanced Space-management Technique for Flash Memory using Reallocation Blocks (재할당 블록을 이용한 플래시 메모리를 위한 효율적인 공간 관리 기법)

  • Kwon, Se-Jin;Chung, Tae-Sun
    • Journal of KIISE:Computing Practices and Letters
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    • v.13 no.7
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    • pp.476-487
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    • 2007
  • Flash memory offers attractive features, such as non-volatile, shock resistance, fast access, and low power consumption for data storage. However, it has one main drawback of requiring an erase before updating the contents. Furthermore, flash memory can only be erased limited number of times. To overcome limitations, flash memory needs a software layer called flash translation layer (FTL). The basic function of FTL is to translate the logical address from the file system like file allocation table (FAT) to the physical address in flash memory. In this paper, a new FTL algorithm called an efficient and advanced space-management technique (EAST) is proposed. EAST improves the performance by optimizing the number of log blocks, by applying the state transition, and by using reallocation blocks. The results of experiments show that EAST outperforms FAST, which is an enhanced log block scheme, particularly when the usage of flash memory is not full.

Diminishing FTL Log Area Searching Cost Using the Counting Bloom Filter (카운팅 블룸 필터를 활용한 FTL 로그영역 탐색 비용 감소)

  • Kang, Woon-Hak;Lee, Sang-Won
    • Proceedings of the Korea Information Processing Society Conference
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    • pp.71-72
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    • 2009
  • 플래시 메모리은 많은 부분에서 기존의 저장장치인 HDD에 비해 좋은 성능을 지녔다. 하지만 HDD와는 달리 데이터의 덮어쓰기가 허용 되지 않는다. 이 문제를 해결하기 위해 플래시 메모리는 FTL(Flash Translation Layer)을 사용하고 있으며, FTL을 통해 기존의 저장장치와 동일하게 사용할 수 있다. FTL들 중 로그영역을 사용하여 성능을 개선한 것들이 많은데, 로그영역의 사용으로 인해 읽기/쓰기 작업시 반드시 로그영역을 탐색을 해야만 했다. 본 논문에서는 카운팅 블룸필터(Counting bloom filter)를 활용하여 불필요한 로그영역 탐색을 줄이는 기법을 제안하였고, 실험을 통해 로그영역에 최신 데이터가 없는 경우 탐색횟수를 크게 줄일 수 있는 것을 확인하였다.

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A Clustered Flash Translation Layer for Mobile Storage Systems (휴대용 저장장치 시스템을 위한 Clustered Flash Translation Layer)

  • Park, Kwang-Hee;Kim, Deok-Hwan
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.45 no.3
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    • pp.94-100
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    • 2008
  • It is necessary to develop the flash memory system software FTL(Flash Translation Layer) which is used in mobile storage like Compact Flash memory. In this paper, we design the FTL using clustered hash table and two phase software caching method to translate logical address into physical address fastly. The experimental results show that the address translation performance of CFTL is 13.3% higher than that of NFTL and 8% higher than that of AFTL, and the memory usage of CFTL is 75% smaller than that of AFTL.

Performance Analysis of FTL Algorithms in Flash Memory for Windows File Systems (윈도우즈(Windows) 파일 시스템에서 플래시 메모리의 FTL(Flash Translation Layer) 알고리즘 성능 분석)

  • Park Won-Joo;Yoo Hyun-Seok;Park Sung-Hwan;Kim Do-Yun;Park Sangwon
    • Proceedings of the Korean Information Science Society Conference
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    • pp.823-825
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    • 2005
  • 이동 기기의 저장장치로 널리 사용되고 있는 플래시 메모리는 하드웨어적 특성으로 인하여 쓰기 전 소거(erase before write) 기법이 사용되고 있다. 이러한 특성으로 인하여 플래시 메모리에서는 성능을 증진시키기 위한 기법이 필요하게 되었으며, 이러한 소프트웨어 모듈을 FTL이라 한다. 플래시 메모리의 용량이 크게 늘어나면서 디스크를 대체할 제품이 등장하고 있으며, 이러한 디스크가 일반 컴퓨터에서의 저장장치로 채택되는 경우가 많아지고 있다. 본 연구에서는 플래시 메모리 기반의 디스크를 이용한 윈도우 파일 시스템에서의 여러 FTL 알고리즘의 성능을 분석, 비교하고, FTL 알고리즘의 올바른 개선 방향을 제시한다.

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De-fragmentation Scheme Exploiting Merge Operation in Flash Memory-based File System (플래시 메모리 기반 파일 시스템에서 병합동작을 이용한 조각 모음 기법)

  • Hyun, Choul-Seung;Lee, Dong-Hee
    • Proceedings of the Korean Information Science Society Conference
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    • pp.377-380
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    • 2007
  • 플래시 메모리는 무게, 내구성, 전력 소비량 측면에서 기존 디스크보다 우수하기 때문에 주로 휴대용 기기의 저장장치로 사용되었다. 최근에는 집적도가 향상되면서 SSD(Solid State Disk)형태로 노트북에서도 활용되고 있다. 이러한 플래시 메모리는 제자리 갱신이 불가능한 특징 때문에 저장장치로 사용하기 위해서는 FTL(Flash Memory Translation Layer)이라는 주소사상 소프트웨어가 필요하다. 그리고 FTL은 블록을 재활용하기 위해 병합 연산을 수행하게 되는데 이 병합 연산의 비용이 시스템 성능에 큰 영향을 미친다. 아울러 FTL 상에서 동작하는 파일 시스템의 경우도 디스크 기반 파일 시스템과 같이 단편화 문제로 인한 성능 저하가 발생하게 된다. 본 논문에서는 플래시 메모리 기반 파일 시스템에서 단편화 현상을 줄이기 위해 FTL의 병합동작의 특성을 활용한 조각 모음 기법을 제안한다. 실험결과는 제안한 기법이 결국 FTL에서 병합 연산의 비용을 줄임으로써 성능을 향상시킬 수 있음을 보여준다.

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Anticipatory I/O Management for Clustered Flash Translation Layer in NAND Flash Memory

  • Park, Kwang-Hee;Yang, Jun-Sik;Chang, Joon-Hyuk;Kim, Deok-Hwan
    • ETRI Journal
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    • v.30 no.6
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    • pp.790-798
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    • 2008
  • Recently, NAND flash memory has emerged as a next generation storage device because it has several advantages, such as low power consumption, shock resistance, and so on. However, it is necessary to use a flash translation layer (FTL) to intermediate between NAND flash memory and conventional file systems because of the unique hardware characteristics of flash memory. This paper proposes a new clustered FTL (CFTL) that uses clustered hash tables and a two-level software cache technique. The CFTL can anticipate consecutive addresses from the host because the clustered hash table uses the locality of reference in a large address space. It also adaptively switches logical addresses to physical addresses in the flash memory by using block mapping, page mapping, and a two-level software cache technique. Furthermore, anticipatory I/O management using continuity counters and a prefetch scheme enables fast address translation. Experimental results show that the proposed address translation mechanism for CFTL provides better performance in address translation and memory space usage than the well-known NAND FTL (NFTL) and adaptive FTL (AFTL).

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