• Title/Summary/Keyword: FTL

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An Address Translation Technique Large NAND Flash Memory using Page Level Mapping (페이지 단위 매핑 기반 대용량 NAND플래시를 위한 주소변환기법)

  • Seo, Hyun-Min;Kwon, Oh-Hoon;Park, Jun-Seok;Koh, Kern
    • Journal of KIISE:Computing Practices and Letters
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    • v.16 no.3
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    • pp.371-375
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    • 2010
  • SSD is a storage medium based on NAND Flash memory. Because of its short latency, low power consumption, and resistance to shock, it's not only used in PC but also in server computers. Most SSDs use FTL to overcome the erase-before-overwrite characteristic of NAND flash. There are several types of FTL, but page mapped FTL shows better performance than others. But its usefulness is limited because of its large memory footprint for the mapping table. For example, 64MB memory space is required only for the mapping table for a 64GB MLC SSD. In this paper, we propose a novel caching scheme for the mapping table. By using the mapping-table-meta-data we construct a fully associative cache, and translate the address within O(1) time. The simulation results show more than 80 hit ratio with 32KB cache and 90% with 512KB cache. The overall memory footprint was only 1.9% of 64MB. The time overhead of cache miss was measured lower than 2% for most workload.

A File Clustering Algorithm for Wear-leveling (마모도 평준화를 위한 File Clustering 알고리즘)

  • Lee, Taehwa;Cha, Jaehyuk
    • Journal of Digital Contents Society
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    • v.14 no.1
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    • pp.51-57
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    • 2013
  • Storage device based on Flash Memory have many attractive features such as high performance, low power consumption, shock resistance, and low weight, so they replace HDDs to a certain extent. An Storage device based on Flash Memory has FTL(Flash Translation Layer) which emulate block storage devices like HDDs. A garbage collection, one of major functions of FTL, effects highly on the performance and the lifetime of devices. However, there is no de facto standard for new garbage collection algorithms. To solve this problem, we propose File Clustering Algorithm. File Clustering Algorithm respect to update page from same file at the same time. So, these are clustered to same block. For this mechanism, We propose Page Allocation Policy in FTL and use MIN-MAX GAP to guarantee wear leveling. To verify the algorithm in this paper, we use TPC Benchmark. So, The performance evaluation reveals that the proposed algorithm has comparable result with the existing algorithms(No wear leveling, Hot/Cold) and shows approximately 690% improvement in terms of the wear leveling.

The Design Status of the Irradiation Facility for Fuel Test (핵연료 시험용 노내조사시험설비의 설계 현황)

  • Park, Kook-Nam;Sim, Bong-Shick;Ahn, Sung-Ho;Yoo, Seong-Yeon
    • Proceedings of the SAREK Conference
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    • 2007.11a
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    • pp.310-315
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    • 2007
  • The FTL has been developed to be able to irradiate test fuels at the irradiation hole(IR1 hole) by considering its utility and user's irradiation requirements. FTL consists of In-Pile Test Section (IPS) and Out-of-Pile System (OPS). Test condition in IPS such as pressure, temperature and the water quality, can be controlled by OPS. For safety assurance IPS is designed to have dual stainless steel pressure vessel and OPS is composed of main cooling water system, emergency cooling water system, LMP(letdown, make-up, purification) system, etc. FTL Conceptual design was set up in 2001, basic design had completed including a design requirement, basic piping & instrument diagram (P&ID), and the detail design in 2004. In 2005, the development team carried out purchase and manufacture hardware and make a contract for construction work. FTL construction work began on August, 2006 and ended on March, 2007. After FTL development which is expected to be finished by 2008, FTL will be used for the irradiation test of the new PWR-type fuel and can maximize the usage of HANARO.

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An In-Depth Analysis and Improvement on Cache Mechanisms of SSD FTL (SSD FTL의 캐시 메커니즘에 대한 심층 분석 및 개선)

  • Lee, Hyung-Bong;Chung, Tae-Yun
    • IEMEK Journal of Embedded Systems and Applications
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    • v.15 no.1
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    • pp.9-16
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    • 2020
  • Recently, the capacity of SSD has been increasing rapidly due to the improvement of flash memory density. To take full advantage of these SSDs, first of all, FTL's prompt adaptation is necessary. The FTL is a translation layer existing in SSDs to overcome the drawback of the SSD that cannot be modified in place, and has garbage collection and caching functions in addition to the map table management function. In this study, we focus on caching function, compare and analyze the cache implementation methodologies, and propose improved methods. Typical cache implementations divide the cache into groups, manage and retrieve the caches in the group as a linked list. Thus, searches are made in the order of the linked list. In contrast, we propose a method of sequential searching using the search area group of a cache registered in the map table regardless of the linked list and cache group. Experimental results show that the proposed method has a 2.5 times improvement over the conventional method.

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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Dynamic Cache Management Scheme on Demand-Based FTL Considering Data Access Pattern (데이터 접근 패턴을 고려한 요구 기반 FTL 내 캐시의 동적 관리 기법)

  • Lee, Bit-Na;Song, Nae-Young;Koh, Kern
    • Proceedings of the Korean Information Science Society Conference
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    • 2011.06a
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    • pp.547-550
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    • 2011
  • 플래시 메모리는 낮은 전력 소비와 높은 성능으로 인해 휴대용 기기에 널리 사용되고 있다. FTL은 플래시 내 자료를 관리하는 소프트웨어 계층으로 플래시 전체의 성능에 영향을 끼친다. 그 중 페이지 레벨 매핑 기법을 적용한 FTL은 유연성이 높고 속도가 빠르나 주소 변환 테이블의 크기가 큰 단점이 있다. 이를 해결하기 위해 자주 접근되는 영역의 매핑 주소만을 매핑 테이블 캐시에 올려놓는 Demand-based FTL(DFTL)이 제안되었다. DFTL 에서는 CMT(Cache Mapping Table)의 참조율이 떨어지는 경우 빈번한 플래시 메모리 접근 오버헤드가 발생하게 된다. 이러한 문제는 흔히 발생하는 일반적인 순차 접근에서조차 문제가 된다. 이에 본 논문에서는 저장 장치의 접근 패턴을 예측하여 CMT의 참조 엔트리를 미리 읽어오는 기법을 제안한다. 제안하는 기법은 저장 장치 접근 패턴의 순차성을 판단하여 연속된 매핑 주소를 미리 CMT에 올려놓고, 읽어오는 매핑 주소 엔트리의 양은 동적으로 관리한다. 추가적으로 CMT에서 발생하는 스래싱(thrashing) 을 파악하기 위해 쫓겨나는 희생 엔트리의 접근 여부를 분석하여 이를 활용하였다. 실험 결과에서 본 기법은 기존의 DFTL에 비해 약간의 공간 오버헤드와 함께 평균 50% 증가한 참조율을 보였다.

SSR (Simple Sector Remapper) the fault tolerant FTL algorithm for NAND flash memory

  • Lee, Gui-Young;Kim, Bumsoo;Kim, Shin-han;Byungsoo Jung
    • Proceedings of the IEEK Conference
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    • 2002.07b
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    • pp.932-935
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    • 2002
  • In this paper, we introduce new FTL(Flash Translation Layer) driver algorithm that tolerate the power off errors. FTL driver is the software that provide the block device interface to the upper layer software such as file systems or application programs that using the flash memory as a block device interfaced storage. Usually, the flash memory is used as the storage devices of the mobile system due to its low power consumption and small form factor. In mobile system, the state of the power supplement is not stable, because it using the small sized battery that has limited capacity. So, a sudden power off failure can be occurred when we read or write the data on the flash memory. During the write operation, power off failure may introduce the incomplete write operation. Incomplete write operation denotes the inconsistency of the data in flash memory. To provide the stable storage facility with flash memory in mobile system, FTL should provide the fault tolerance against the power off failure. SSR (Simple Sector Remapper) is a fault tolerant FTL driver that provides block device interface and also provides tolerance against power off errors.

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Design of an Efficient FTL Algorithm Exploiting Locality Based on Sector-level Mapping (Locality를 이용한 섹터 매핑 기법의 효율적인 FTL 알고리듬)

  • Hong, Soo-Jin;Hwang, Sun-Young
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.7B
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    • pp.818-826
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    • 2011
  • This paper proposes a novel FTL (Flash Translation Layer) algorithm employing sector-level mapping technique based on locality to reduce the number of erase operations in flash memory accesses. Sector-level mapping technique shows higher performance than other mapping techniques, even if it requires a large mapping table. The proposed algorithm reduces the size of mapping table by employing dynamic table update, processes sequential writes by exploiting sequential locality and extracts hot sector in random writes. Experimental results show that the number of erase operations has been reduced by 75.4%, 65.8%, and 10.3% respectively when compared with well-known BAST, FAST and sector mapping algorithms.

Robustness Analysis of Flash Memory Software using Fault Injection Tests (폴트 삽입 테스트를 이용한 플래시 메모리 소프트웨어의 강건성 분석)

  • Lee, Dong-Hee
    • Journal of KIISE:Computing Practices and Letters
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    • v.11 no.4
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    • pp.305-311
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    • 2005
  • Flash memory software running on cellular phones and PDAs need to be tested extensively to cope with abrupt power and media faults. For those tests, we designed and implemented a Flash memory emulator with fault injection features. The fault injection tester has provided a helpful framework for designing fault recovery schemes and also for analyzing fault damages to the FTL (Flash Translation Layer) and file system for a Flash memory based system. In this paper, we discuss Plash memory fault types and fault injection features implemented on this Flash memory emulator. We then discuss in detail a design flaw revealed during fault injection tests. Specifically, it was revealed that a scheme that was believed to improve reliability instead, turned out to be harmful. In addition, we discuss post-fault behaviors of the FTL and the file system.

A Multi-level Mapping Table Scheme for SSD (SSD를 위한 다단계 사상 테이블 기법)

  • Yang, Soo-Hyeon;Ryu, Yeonseung
    • Proceedings of the Korea Information Processing Society Conference
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    • 2010.11a
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    • pp.1591-1594
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    • 2010
  • NAND 플래시 메모리 기반의 Solid State Disk (SSD)의 내부에는 Flash Translation Layer (FTL)이라는 소프트웨어가 사용되고 있다. FTL은 파일 시스템으로부터 요청되는 논리 주소를 플래시 메모리의 물리 주소로 변환하며 이를 위하여 사상 테이블을 사용한다. 사상 테이블의 빠른 접근을 위하여 사상 테이블은 SSD 내부의 RAM에 유지하는데 SSD의 용량이 커지게 되면 사상 테이블로 인해 요구되는 RAM의 크기도 커지는 문제점이 있다. 본 논문에서는 FTL의 사상 테이블을 페이지 단위로 나누어 필요할 때마다 RAM에 적재하는 다단계 사상 테이블 기법을 연구하였다.