• Journal of Digital Contents Society
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• v.14 no.2
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• pp.215-222
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• 2013

NAND flash memory-based Solid State Drives (SSD) have lots of merits compared to traditional hard disk drives (HDD). However, random write in SSD is still far slower than sequential read/write and random read. There are two independent approaches to resolve this problem: 1) using part of the flash memory blocks as log blocks, and 2) using internal write buffer (DRAM or Non-Volatile RAM) in SSD. While log blocks are managed by the Flash Translation Layer (FTL), write buffer management has been treated separately from FTL. Write buffer management schemes did not use the exact status of log blocks and log block management schemes in FTL did not consider the behavior of write buffer management scheme. In this paper, we first show that log blocks and write buffer have a tight relationship to each other, which necessitates integrated management of both of them. Since log blocks also can be viewed as another type of write buffer, we can manage both of them as an integrated write buffer. Then we provide three design criteria for the integrated write buffer management scheme which can be very useful to SSD firmware designers.

• The KIPS Transactions:PartA
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• v.12A no.3 s.93
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• pp.205-214
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• 2005

Flash memory is at high speed used as storage of personal information utilities, ubiquitous computing environments, mobile phones, electronic goods, etc. This is because flash memory has the characteristics of low electronic power, non-volatile storage, high performance, physical stability, portability, and so on. However, differently from hard disks, it has a weak point that overwrites on already written block of flash memory is impossible to be done. In order to make an overwrite possible, an erase operation on the written block should be performed before the overwrite, which lowers the performance of flash memory highly. In order to solve this problem the flash memory controller maintains a system software module called the flash translation layer(FTL). Of many proposed FTL schemes, the log block buffer scheme is best known so far. This scheme uses a small number of log blocks of flash memory as a write buffer, which reduces the number of erase operations by overwrites, leading to good performance. However, this scheme shows a weakness of low page usability of log blocks. In this paper, we propose an enhanced log block buffer scheme, FAST(Full Associative Sector Translation), which improves the page usability of each log block by fully associating sectors to be written by overwrites to the entire log blocks. We also show that our FAST scheme outperforms the log block buffer scheme.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.2
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• pp.90-102
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• 2010

Flash memory has been widely used as an important storage device for consumer electronics. For the flash memory-based storage systems, FTL (Flash Translation Layer) is used to handle the mapping between a logical page address and a physical page address. Especially, log buffer-based FTLs provide a good performance with small-sized mapping information. In designing the log buffer-based FTL, one important factor is to determine the mapping structure between data blocks and log blocks, called associativity. While previous works use static associativity fixed at the design time, we propose a new log block mapping scheme which adjusts associativity based on the run-time workload. Our proposed scheme improves the I/O performance about 5~16% compared to the static scheme by adjusting the associativity to provide the best performance.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.51-56
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• 2009

Flash memory has rapidly deployed as data storage. However, the flash memory has a major disadvantage that recorded data cannot be dynamically overwritten. In order to solve this "erase-before-write" problem, the log block buffer scheme used Flash memory file system. however, the current managements of the log buffer, in case random write pattern, BAST technique have problem of frequent merge operation, but FAST technique don't consider merge operation by frequently updated data. Previous methods not consider merge operation cost and frequently updated data. In this paper, we propose a new log buffer management scheme, called JBB. Our proposed method evaluates the worth of the merge of log blocks, so we conducts the merge operation between infrequently updated data and its data blocks, and postpone the merge operation between frequently updated data and its data blocks. Through the method, we prevent the unnecessary merge operations, reduce the number of the erase operation, and improve the utilization of the flash memory storage. We show the superiority of our proposed method through the performance evaluation with BAST and FAST.

• Journal of KIISE:Databases
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• v.37 no.5
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• pp.238-249
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• 2010

Flash memory has been studied as a storage medium in order to improve the performance of the system using its high computing speed in the DBMS field where frequent data access is needed. The most difficulty using the flash memory is the performance degradation and the life span shortening of flash memory coming from inefficient in-place update. Log based approaches have been studied to solve inefficient in-place update problem in the DBMS where write operations occur in smaller size of data than page frequently. However the existing log based approaches suffer from the frequent merging operations, which are the principal cause of performance deterioration. Thus is because their fixed log area management can not guarantee a sufficient space for logs. In this paper, we propose non-fixed log area management technique that can minimize the occurrence of the merging operations by promising an enough space for logs. We also suggest the cost calculation model of the optimal log sector number minimizing the system operation cost in a block. In experiment, we show that our non-fixed log area management technique can have the improved performance compared to existing approaches.

• Journal of KIISE:Databases
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• v.36 no.5
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• pp.374-385
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• 2009

Flash memory becomes increasingly popular as data storage for various devices because of its versatile features such as non-volatility, light weight, low power consumption, and shock resistance. Flash memory, however, has some distinct characteristics that make today's disk-based database technology unsuitable, such as no in-place update and the asymmetric speed of read and write operations. As a result, most traditional disk-based database systems may not provide the best attainable performance on flash memory. To maximize the database performance on flash memory, some approaches have been proposed where only the changes made to the database, i.e., logs, are written to another empty place that has born erased in advance. In this paper, we propose an efficient log management scheme for flash-based database systems. Unlike the previous approaches, the proposed approach stores logs in specially allocated blocks, called log blocks. By evenly distributing logs across log blocks, the proposed approach can significantly reduce the number of write and erase operations. Our performance evaluation shows that the proposed approaches can improve the overall system performance by reducing the number of write and erase operation compared to the previous ones.

• The Journal of the Korea Contents Association
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• v.10 no.1
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• pp.68-77
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• 2010

In this paper, we propose a new log buffer management scheme considering the accessibility of the data. Our proposed scheme evaluates the worth of the merge of log blocks. It conducts the merge operations between infrequently updated data and the data blocks and postpones as much as possible the merge operations between frequently updated data and the data blocks. As a result, the proposed method prevents the unnecessary merge operations, reduces the number of the erase operations, and improves the utilization of the flash memory storage. In order to show the superiority of the proposed scheme, we compare it with BAST and FAST. It is shown through performance evaluation that the proposed method achieves about 25% and 65% performance improvements over BAST and FAST on average in terms of the number of the erase operations.

• Proceedings of the Korea Information Processing Society Conference
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• 2019.10a
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• pp.31-33
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• 2019

시스템을 안정적으로 운용하기 위해서는 신뢰성 기반의 로그관리시스템이 필요하다. 모든 이력이 기록되는 로그의 위·변조를 방지하기 위해 로그 정보를 블록체인 기술로 관리하여 어떠한 상황에서도 시스템 이력을 신뢰할 수 있는 서비스를 제안한다. Hyplerledger Fabric을 사용하여 인증 관리 시스템에 의해 허가된 사용자만이 접근할 수 있다. 또한 분산원장에 한 번 기록된 로그 파일은 더 이상 수정하거나 삭제될 수 없다. 이 시스템을 활용하면 로그 파일의 위·변조 여부를 판단하는데 발생하는 시간, 비용, 불확실성을 크게 줄일 수 있을 것으로 기대된다.

• KIPS Transactions on Computer and Communication Systems
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• v.9 no.7
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• pp.143-148
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• 2020

Recently, web services have been expanded to various areas with the evolution of cloud environment. Whenever a user accesses a web service, the user's log information is stored in the web server. This log information is used as data to analyze the user's web service tendencies and is also used as important data to track the user's system access when a security problem in the system occurs. Currently, most web servers manage user log information in a centralized manner. When user log information is managed in a centralized manner, it is simple in the side of operation, but has a disadvantage of being very vulnerable to external malicious attacks. In the case of centralized management, user log information stored in the web server can be arbitrarily manipulated by external attacks, and in severe cases, the manipulated information can be leaked. In this case, it not only decreases the trust of the web service, but also makes it difficult to trace the source and cause of the attack on the web server. In order to solve these problems, this paper proposes a new method of managing user log information in a cloud environment by applying blockchain technology as an alternative to the existing centralized log management method. The proposed method can manage log information safely from external attacks because user log information is distributed and stored in blockchain on a private network with cloud environment.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.11a
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• pp.70-72
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• 2014

플래시 메모리는 소형 저장 장치뿐만 아니라 대용량 저장장치까지 응용되고 있다. 하지만 기존의 하드디스크 (HDD)와 다르게 플래시 메모리는 읽기, 쓰기, 소거 연산의 속도가 다르고 쓰기 전 지우기(erase before write)라는 특성 때문에 FTL의 한 메커니즘인 GC (Garbage Collection)를 수행할 때 많은 오버헤드가 발생한다. 이에 이 논문은 DRAM의 공간을 효율적으로 활용하고 유효한 페이지 복사와 소거 연산의 횟수를 줄여 전체적인 플래시 메모리 GC 오버헤드를 줄이기 위한 블록 링크드 리스트 기법을 제안한다. 블록 링크드 리스트 기법은 같은 LBN에 해당하는 데이터를 로그 블록에 적고 해당 로그 블록들을 링크드 리스트로 관리해 소거 연산을 미룰 수 있다. 링크드 리스트들에 관한 정보는 DRAM에 테이블 형태로 적는다. 이때 테이블에는 블록 주소들이 적히므로 페이지 단위로 링크드 리스트를 관리하는 다른 기법에 비해 DRAM의 공간을 효율적으로 활용하게 된다.