• Proceedings of the Korean Information Science Society Conference
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• 2012.06c
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• pp.72-74
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• 2012

최근 스마트폰, 태블릿이 보편화되고 플래시 메모리가 모바일기기의 저장장치로 많이 사용되면서 저장되는 데이터에 대한 보안성도 높아지고 있다. 모바일 기기를 사용하는 사용자 입장에서 더 이상 필요치 않은 목적으로 데이터를 삭제하고 유출을 막기 위해 파일 와이핑 기법을 사용한다. 하지만 일반적인 와이핑 기법은 하드디스크 특성을 바탕으로 수행되기 때문에 플래시 메모리를 사용할 경우 플래시 메모리 특성으로 인해 와이핑 이후 기존정보가 존재하기 때문에 복구가 가능하다. 최근 플래시 메모리 데이터의 보안성을 요구하는 기법이 연구된바 있지만 불필요한 오버헤드 및 기법 적용이 제한적이라는 문제가 있다. 본 논문에서는 다양한 FTL에 적용이 가능한 플래시 메모리상의 저장된 데이터에 대한 와이핑 수행이후 복구 방지 기법을 제안한다. 이 기법은 임의 값을 이용한 블록 치환 알고리즘을 통해 테이블을 생성하고 테이블을 이용해서 플래시 메모리를 블록 단위로 치환을 하여 수행한다.

• 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.

• Journal of the Semiconductor & Display Technology
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• v.21 no.1
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• pp.85-90
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• 2022

In this paper, an asynchronous nonvolatile memory module using a self-diagnosis function was designed. For the system to work, a lot of data must be input/output, and memory that can be stored is required. The volatile memory is fast, but data is erased without power, and the nonvolatile memory is slow, but data can be stored semi-permanently without power. The non-volatile static random-access memory is designed to solve these memory problems. However, the non-volatile static random-access memory is weak external noise or electrical shock, data can be some error. To solve these data errors, self-diagnosis algorithms were applied to non-volatile static random-access memory using error correction code, cyclic redundancy check 32 and data check sum to increase the reliability and accuracy of data retention. In addition, the possibility of application to an asynchronous non-volatile storage system requiring reliability was suggested.

• Journal of the Semiconductor & Display Technology
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• v.22 no.1
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• pp.43-48
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• 2023

This paper discusses the design of 32Mbyte asynchronous nonvolatile memory modules, which includes self-diagnosis and RTC (Real Time Clock) functions to enhance their data stability and reliability. Nonvolatile memory modules can maintain data even in a power-off state, thereby improving the stability and reliability of a system or device. However, due to the possibility of data error due to electrical or physical reasons, additional data loss prevention methods are required. To minimize data error in asynchronous nonvolatile memory modules, this paper proposes the use of voltage monitoring circuits, self-diagnosis, BBT (Bad Block Table), ECC (Error Correction Code), CRC (Cyclic Redundancy Check)32, and data check sum, data recording method using RTC. Prototypes have been produced to confirm correct operation and suggest the possibility of commercialization.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.05a
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• pp.525-526
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• 2023

최근 빅데이터를 처리하기 위한 고용량의 저장장치의 연구가 활발하게 진행되고 있다. 특히 낸드 플래시 메모리 기반 저장장치인 SSD(Solid State Drive)는 고속 데이터 처리가 가능하기 때문에 다양한 저장 시스템에서 사용되고 있다. 그러나 낸드 플래시 메모리는 읽기 속도가 빠르고 쓰기 속도가 느린 비대칭 구조를 가지고 있어 데이터 쓰기 작업이 진행 중일 때 다른 작업이 대기하게 되어 전체적인 시스템 성능에 영향을 미칠 수 있다. 이에 대해 대부분의 연구에서는 쓰기 성능을 개선하기 위한 버퍼 관리 정책들이 제안되었다. 기술의 발전으로 쓰기 성능은 개선되었지만, 그에 비해 읽기 성능이 저조한 문제가 있다. 본 논문에서는 읽기 성능이 쓰기 성능보다 취약한 점을 분석하고 플래시 메모리 내에 저장장치 속도를 개선하기 위해 앞으로 읽기 요청 가능성이 있는 예상 데이터를 선형회귀 모델을 적용하여 전송 대기 시간 중 미리 읽는 정책을 제안한다.

• Journal of IKEEE
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• v.22 no.4
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• pp.1168-1174
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• 2018

For the initial state of NAND flash memories, error-free and single-error cases are dominant due to a good channel environment on memory cells. It is important to deal with such cases, which affects the overall system performance. However, the conventional schemes for polar codes equally decode the codes even for the error-free and single-error cases since they cannot classify and decode separately. In this paper, a new pre-processing scheme for polar codes is proposed so as to improve the overall decoding latency by decoding the frequent error-free and single-error cases. Before the ordinary decoding process, the proposed scheme first decodes the frequent error-free and single-error cases. According to the experimental results, the proposed pre-processing scheme decreases the average decoding latency by 64% compared to the conventional scheme for (1024, 512) polar codes.

• The Journal of the Korea Contents Association
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• v.16 no.10
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• pp.477-482
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• 2016

This paper presents a new method of parity storing for ECC(error correcting code) in SSD (solid-state drive) and suitable structure of the controller. In general usage of NAND flash memory, we partition a page into data and spare area. ECC parity is stored in the spare area. The method has overhead on area and timing due to access of the page memory discontinuously. This paper proposes a new parity policy storing method that reduces overhead and R(read)/W(write) timing by using whole page area continuously without partitioning. We analyzed overhead and R/W timing. As a result, the proposed parity storing has 13.6% less read access time than the conventional parity policy with 16KB page size. For 4GB video file transfer, it has about a minute less than the conventional parity policy. It will enhance the system performance because the read operation is key function in SSD.

• Journal of Digital Convergence
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• v.20 no.3
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• pp.343-348
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• 2022

Recently, With the recent rapid development of technology, the amount of data generated by various systems is increasing, and enterprise servers and data centers that have to handle large amounts of big data need to apply high-stability and high-performance storage devices even if costs increase. In such systems, SSD(solid state disk) that provide high performance of read/write are often used as storage devices. However, due to the characteristics of reading and writing on a page-by-page basis, erasing operations on a block basis, and erassing-before-writing, there is a problem that performance is degraded when duplicate writes occur. Therefore, in order to delay this performance degradation problem, over-provision technology of SSD has been applied internally. However, since over-provided technologies have the disadvantage of consuming a lot of storage space instead of performance, the application of inefficient technologies above the right performance has a problem of over-costing. In this paper, we proposed a method of measuring the performance and cost incurred when various over-provisions are applied in an SSD and predicting the system-optimized over-provided ratio based on this. Through this research, we expect to find a trade-off with costs to meet the performance requirements in systems that process big data.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.2
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• pp.241-245
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• 2008

Non-volatile RAM (NVRAM) has both characteristics of nonvolatility and byte addressability. In order to efficiently exploit this NVRAM in the file system layer, we proposed the MiNV (Metadata in NVram) file system in our previous research. MiNV file system maintains all the metadata in NVRAM while storing file data in NAND Flash memory. In this paper, we experimentally analyze the efficiency for the execution of garbage collection in the MiNV file system. Also, we quantify the file system performance gains obtained from efficient garbage collection. Experimental results show that garbage collection on the MiNV file system executes more efficiently that on YAFFS even though these file systems adopt exactly the same garbage collection policy. Specifically, the MiNV file system invokes the aggressive garbage collection mechanism less frequently than YAFFS. Additionally, the MiNV file system postpones the first execution of the aggressive garbage collection mechanism in our experiments. From the experiments, we verify that the efficiency of garbage collection leads to performance improvements of the MiNV file system.

• Journal of Information Technology Services
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• v.12 no.4
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• pp.369-380
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• 2013

The advent of the state-of-the-art technologies such as cloud computing and big data processing stimulates the provision of various new IT services, which implies that more servers are required to support them. However, the need for more servers will lead to more energy consumption and the efficient use of energy in the computing environment will become more important. The next generation nonvolatile RAM has many desirable features such as byte addressability, low access latency, high density and low energy consumption. There are many approaches to adopt them especially in the area of the file system involving storage devices, but their focus lies on the improvement of system performance, not on energy reduction. This paper suggests a novel approach for energy reduction in which the MRAM-based SSD is utilized as a storage device instead of the hard disk and a downsized page is adopted instead of the 4KB page that is the size of a page in the ordinary file system. The simulation results show that energy efficiency of a new approach is very effective in case of accessing the small number of bytes and is improved up to 128 times better than that of NAND Flash memory.