• Title, Summary, Keyword: FTL

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Cost-based Optimization of Block Recycling Scheme in NAND Flash Memory Based Storage System (NAND 플래시 메모리 저장 장치에서 블록 재활용 기법의 비용 기반 최적화)

  • Lee, Jong-Min;Kim, Sung-Hoon;Ahn, Seong-Jun;Lee, Dong-Hee;Noh, Sam-H.
    • Journal of KIISE:Computing Practices and Letters
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    • v.13 no.7
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    • pp.508-519
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    • 2007
  • Flash memory based storage has been used in various mobile systems and now is to be used in Laptop computers in the name of Solid State Disk. The Flash memory has not only merits in terms of weight, shock resistance, and power consumption but also limitations like erase-before-write property. To overcome these limitations, Flash memory based storage requires special address mapping software called FTL(Flash-memory Translation Layer), which often performs merge operation for block recycling. In order to reduce block recycling cost in NAND Flash memory based storage, we introduce another block recycling scheme which we call migration. As a result, the FTL can select either merge or migration depending on their costs for each block recycling. Experimental results with Postmark benchmark and embedded system workload show that this cost-based selection of migration/merge operation improves the performance of Flash memory based storage. Also, we present a solution of macroscopic optimal migration/merge sequence that minimizes a block recycling cost for each migration/merge combination period. Experimental results show that the performance of Flash memory based storage can be more improved by the macroscopic optimization than the simple cost-based selection.

Index block mapping for flash memory system (플래쉬 메모리 시스템을 위한 인덱스 블록 매핑)

  • Lee, Jung-Hoon
    • Journal of the Korea Society of Computer and Information
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    • v.15 no.8
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    • pp.23-30
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    • 2010
  • Flash memory is non-volatile and can retain data even after system is powered off. Besides, it has many other features such as fast access speed, low power consumption, attractive shock resistance, small size, and light-weight. As its price decreases and capacity increases, the flash memory is expected to be widely used in consumer electronics, embedded systems, and mobile devices. Flash storage systems generally adopt a software layer, called FTL. In this research, we proposed a new FTL mechanism for overcoming the major drawback of conventional block mapping algorithm. In addition to the block mapping table, a index block mapping table with a small size is used to indicate sector location. The proposed indexed block mapping algorithm by adding a small size. By the simulation result, the proposed FTL provides an enhanced speed than a conventional hybrid mapping algorithm by around 45% in average, and the requirement of mapping memory is also reduced by around 12%.

Efficient Prefetching and Asynchronous Writing for Flash Memory (플래시 메모리를 위한 효율적인 선반입과 비동기 쓰기 기법)

  • Park, Kwang-Hee;Kim, Deok-Hwan
    • 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.

An Efficient Page-Level Mapping Algorithm for Handling Write Requests in the Flash Translation Layer by Exploiting Temporal Locality (플래시 변환 계층에서 시간적 지역성을 이용하여 쓰기 요청을 처리하는 효율적인 페이지 레벨 매핑 알고리듬)

  • Li, Hai-Long;Hwang, Sun-Young
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.41 no.10
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    • pp.1167-1175
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    • 2016
  • This paper proposes an efficient page-level mapping algorithm that reduces the erase count in the FTL for flash memory systems. By maintaining the weight for each write request in the request buffer, the proposed algorithm estimates the degree of temporal locality for each incoming write request. To exploit temporal locality deliberately for determination of hot request, the degree of temporal locality should be much higher than the reference point determined experimentally. While previous LRU algorithm treats a new write request to have high temporal locality, the proposed algorithm allows write requests that are estimated to have high temporal locality to access hot blocks to store hot data intensively. The pages are more frequently updated in hot blocks than warm blocks. A hot block that has most of invalid pages is always selected as victim block at Garbage Collection, which results in delayed erase operation and in reduced erase count. Experimental results show that erase count is reduced by 9.3% for real I/O workloads, when compared to the previous LRU algorithm.

The Efficient Merge Operation in Log Buffer-Based Flash Translation Layer for Enhanced Random Writing (임의쓰기 성능향상을 위한 로그블록 기반 FTL의 효율적인 합병연산)

  • Lee, Jun-Hyuk;Roh, Hong-Chan;Park, Sang-Hyun
    • The KIPS Transactions:PartD
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    • v.19D no.2
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    • pp.161-186
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    • 2012
  • Recently, the flash memory consistently increases the storage capacity while the price of the memory is being cheap. This makes the mass storage SSD(Solid State Drive) popular. The flash memory, however, has a lot of defects. In order that these defects should be complimented, it is needed to use the FTL(Flash Translation Layer) as a special layer. To operate restrictions of the hardware efficiently, the FTL that is essential to work plays a role of transferring from the logical sector number of file systems to the physical sector number of the flash memory. Especially, the poor performance is attributed to Erase-Before-Write among the flash memory's restrictions, and even if there are lots of studies based on the log block, a few problems still exists in order for the mass storage flash memory to be operated. If the FAST based on Log Block-Based Flash often is generated in the wide locality causing the random writing, the merge operation will be occur as the sectors is not used in the data block. In other words, the block thrashing which is not effective occurs and then, the flash memory's performance get worse. If the log-block makes the overwriting caused, the log-block is executed like a cache and this technique contributes to developing the flash memory performance improvement. This study for the improvement of the random writing demonstrates that the log block is operated like not only the cache but also the entire flash memory so that the merge operation and the erase operation are diminished as there are a distinct mapping table called as the offset mapping table for the operation. The new FTL is to be defined as the XAST(extensively-Associative Sector Translation). The XAST manages the offset mapping table with efficiency based on the spatial locality and temporal locality.

Block Unit Mapping Technique of NAND Flash Memory Using Variable Offset

  • Lee, Seung-Woo;Ryu, Kwan-Woo
    • Journal of the Korea Society of Computer and Information
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    • v.24 no.8
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    • pp.9-17
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    • 2019
  • In this paper, we propose a block mapping technique applicable to NAND flash memory. In order to use the NAND flash memory with the operating system and the file system developed on the basis of the hard disk which is mainly used in the general PC field, it is necessary to use the system software known as the FTL (Flash Translation Layer). FTL overcomes the disadvantage of not being able to overwrite data by using the address mapping table and solves the additional features caused by the physical structure of NAND flash memory. In this paper, we propose a new mapping method based on the block mapping method for efficient use of the NAND flash memory. In the case of the proposed technique, the data modification operation is processed by using a blank page in the existing block without using an additional block for the data modification operation, thereby minimizing the block unit deletion operation in the merging operation. Also, the frequency of occurrence of the sequential write request and random write request Accordingly, by optimally adjusting the ratio of pages for recording data in a block and pages for recording data requested for modification, it is possible to optimize sequential writing and random writing by maximizing the utilization of pages in a block.

Hot Data Identification For Flash Based Storage Systems Considering Continuous Write Operation

  • Lee, Seung-Woo;Ryu, Kwan-Woo
    • Journal of the Korea Society of Computer and Information
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    • v.22 no.2
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    • pp.1-7
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    • 2017
  • Recently, NAND flash memory, which is used as a storage medium, is replacing HDD (Hard Disk Drive) at a high speed due to various advantages such as fast access speed, low power, and easy portability. In order to apply NAND flash memory to a computer system, a Flash Translation Layer (FTL) is indispensably required. FTL provides a number of features such as address mapping, garbage collection, wear leveling, and hot data identification. In particular, hot data identification is an algorithm that identifies specific pages where data updates frequently occur. Hot data identification helps to improve overall performance by identifying and managing hot data separately. MHF (Multi hash framework) technique, known as hot data identification technique, records the number of write operations in memory. The recorded value is evaluated and judged as hot data. However, the method of counting the number of times in a write request is not enough to judge a page as a hot data page. In this paper, we propose hot data identification which considers not only the number of write requests but also the persistence of write requests.

File System Featured FAT Compatible Flash Translation Layer (파일시스템 기능을 지원하는 FAT 호환 플래시 변환 계층)

  • Kim, Yumi;Baek, Seungjae;Choi, Jongmoo
    • Proceedings of the Korea Information Processing Society Conference
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    • pp.699-702
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    • 2009
  • 저 전력, 내구성, 소형, 빠른 속도 등의 장점을 가지고 있는 플래시 메모리는 생산 기술 발전에 힘입어 센서 노드, 휴대폰, MP3, PMP등의 소형 전자 제품의 저장장치에서부터 SSD형태로 노트북이나 서버에 이르기 까지 그 활용범위가 더욱 확장되어 가고 있다. 다양한 시스템에서 사용될 수 있는 플래시 메모리의 특성상 이에 저장된 데이터의 호환성은 중요한 고려사항이다. 이를 위해 플래시 메모리의 고유한 특성을 숨기고 일반적인 블록장치로 에뮬레이션 해주는 소프트웨어인 FTL과 FAT 파일시스템이 플래시 메모리 관리를 위한 사실상 표준 소프트웨어로써 사용되고 있다. 그러나 범용 컴퓨터를 기반으로 개발된 FTL과 FAT 파일시스템을 열악한 하드웨어로 구성된 시스템에서 구동하는 경우 많은 제약이 발생한다. 따라서 본 논문에서는 이러한 제약사항을 극복하기 위해 최소한의 파일시스템 기능을 제공하는 FAT 표준 호환 FTL을 제안한다. 제안된 기법은 리눅스 운영체제에 동적으로 적재 가능한 모듈형태로 구현되었으며, 실험을 통해 본 논문에서 제안한 기법이 기존 기법 대비 32%의 메모리 공간을 절약할 수 있으며, 동시에 완벽한 FAT 호환성을 제공함을 확인할 수 있었다.

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Development of Sealing Technology for Instrumentation Feedthrough of High Pressure Vessel (고압용기의 계장선 통과부위 밀봉기술 개발)

  • Jeong, H.Y.;Hong, J.T.;Ahn, S.H.;Joung, C.Y.;Lee, J.M.;Lee, C.Y.
    • Journal of the Korean Society of Mechanical Technology
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    • v.13 no.2
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    • pp.137-143
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    • 2011
  • Fuel Test Loop(FTL) is a facility which could conduct a fuel irradiation test at HANARO(High-flux Advanced Neutron Application Reactor). FTL simulates commercial NPP's operating conditions such as the pressure, temperature and neutron flux levels to conduct the irradiation and thermo-hydraulic tests. The In-Pile Test Section(IPS) installed in HANARO FTL is designed as a pressure vessel design conditions of $350^{\circ}C$, 17.5MPa. The instrumentation MI-cables for thermocouples, SPND and LVDT are passed through the sealing plug, which is in the pressure boundary region and is a part of instrumentation feedthrough of MI-cable. In this study, the brazing method and performance test results are introduced to the sealing plug with BNi-2 filler metal, which is selected with consideration of the compatibility for the coolant. The performance was verified through the insulation resistance test, hydrostatic test, and helium leak test.

A Study of the Merging Layers of the Storage System for Flash-Based DBMS (플래시 메모리용 DBMS를 위한 스토리지 시스템의 계층 통합에 대한 연구)

  • Sim, Hyo-Gi;Yoon, Kyoung-Hon;Park, Sung-Min;Jung, Ho-Young;Cha, Jae-Hyuk;Kang, Soo-Yong
    • Journal of Digital Contents Society
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    • v.8 no.4
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    • pp.593-600
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    • 2007
  • Small computer systems such as mobile devices adopt NAND flash memories as their storage media. However, DBMS running on such systems are optimized to hard disks. When small computer systems use DBMS they usually use additional system layer, like FTL, that emulates flash memories as normal hard disks and DBMS cannot control flash memories directly. In this paper, we propose unified storage system that DBMS controls flash memories directly. We implemented the system in a real environment and proved the proposed system outperforms legacy systems.

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