• Proceedings of the Korean Society of Computer Information Conference
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• 2014.07a
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• pp.353-354
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• 2014

오늘날 데이터베이스 시스템 의 스토리지에 많은 정보를 저장하게 되는데 이때 주로 HDD가 사용되고 있으며, 지금까지 대용량 저장 장치로 발전을 해왔다. HDD는 단위 비트 당 가격이 저렴한 이점이 있으나 HDD를 이용한 저장장치는 낮은 수행 속도 때문에 빠르게 정보를 제공받기를 원하는 사용자의 요구를 충족시키지 못하고 있다. 이를 해결하기 위해 빠른 I/O속도를 갖는 SSD를 이용한 저장 장치가 연구가 많이 되고 있으나 비트 당 가격이 비싼 SSD의 단점으로 인해 HDD를 전부 SSD로 대체하기에는 어려움이 있다. 본 논문에서는 HDD를 SSD로 완전히 대체하는 시스템이 아니라 SSD를 캐시로 사용한 SSD의 기반으로 혼합 스토리지 구조를 이용하여 검색 성능을 최적화시키기 위한 방법을 제안한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.11a
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• pp.165-166
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• 2009

최근 SSD는 빠른 속도와 저전력, 무소음 등의 장점으로 하드디스크를 빠르게 대체하고 있다. 그러나 아직 SSD의 내부 동작 알고리즘이 공개된 바 없으며 SSD의 내부 동작에 대한 설명도 부족하다. 이에 본 논문에서는 실제 SSD에 상반된 패턴을 갖는 작업 부하를 이용하여 성능을 측정하고, SSD 시뮬레이터를 이용하여 측정된 결과를 분석한다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.3
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• pp.176-183
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• 2015

This research proposes a method to estimate the fatigue life of SSD(solid-state drive) due to the effect of dummy solder ball under forced vibration. A finite element model of the SSD was developed to simulate the forced vibration and a modal testing was performed to verify the developed finite element model. Fatigue life of the SSD under vibration was experimentally determined according to JEDEC standard in which the SSD was excited by a sinusoidal sweep vibration within the narrow frequency band around the first natural frequency until the SSD fails. Basquin's equation was introduced to estimate the fatigue life of the SSD due to the effect of dummy solder balls. It shows that the dummy solder balls are effective elements of the SSD to increase the fatigue life of an SSD by increasing 700 times of the fatigue life of the given SSD.

• Journal of KIISE
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• v.42 no.6
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• pp.691-698
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• 2015

Application launch time is an important performance metric to user experience in desktop and laptop environment, which mostly depends on the performance of secondary storage. Application launch times can be reduced by utilizing solid-state drive (SSD) instead of hard disk drive (HDD). However, considering a cost-performance trade-off, utilizing SSDs as caches for slow HDDs is a practicable alternative in reducing the application launch times. We propose a new SSD caching scheme which migrates data blocks from HDDs to SSDs. Our scheme operates entirely in the file system level and does not require an extra layer for mapping SSD-cached data that is essential in most other schemes. In particular, our scheme does not incur mapping overheads that cause significant burdens on the main memory, CPU, and SSD space for mapping table. Experimental results conducted with 8 popular applications demonstrate our scheme yields 56% of performance gain in application launch, when data blocks along with metadata are migrated.

• Korean Journal of Biological Psychiatry
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• v.18 no.4
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• pp.210-216
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• 2011

Subsyndromal depression (SSD) is found to be more prevalent than major depressive disorder (MDD) and minor depressive disorder (MnDD). SSD is also associated with adverse clinical outcomes, increased risk of suicide, increased social dysfunction and disability, increased risk for future mood disorders, and increased uses of medical and mental health services. DSM-IV diagnostic criteria are not suitable for capturing SSD. Although there is no agreement on gold standard to define SSD so far, three definitions of SSD are available. First, SSD is defined as having two or more current depressive symptoms without core depressive symptoms (depressive mood or loss of interest) and with time threshold (most of the day and nearly every day over at least two weeks). Second, SSD is defined as having two or more current depressive symptoms with core depressive symptoms and without time threshold. Third, SSD is defined by using cutoff points of depression rating scales. SSD may represent a prodromal, residual, or interepisode symptomatic state in the course of MDD and MnDD. More than a half of SSD patients became any type of depressive disorders (SSD, MnDD and MDD) at 1 year. SSD may represent a discrete category of its own, without prior or consequent episodes of MDD. Considering clinical significance of SSD such as its high prevalence, significant psychosocial impairment and chronicity and serious outcomes, researchers and clinicians should be more vigilant in capturing and caring for patients with SSD.

• The KIPS Transactions:PartA
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• v.19A no.1
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• pp.35-44
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• 2012

Traditional technologies that are used to improve the performance of hard disk drives show many negative cases if they are applied to solid state drives (SSD). Access time and block sequence in hard disk drives that consist of mechanical components are very important performance factors. Meanwhile, SSD provides superior random read performance that is not affected by block address sequence due to the characteristics of flash memory. Practically, it is recommended to disable prefetching if a SSD is installed in a personal computer. However, this paper presents a combinational method of a prefetching scheme and a memory management that consider the internal structure of SSD and the characteristics of NAND flash memory. It is important that SSD must concurrently operate multiple flash memory chips. The I/O unit size of NAND flash memory tends to increase and it exceeded the block size of operating systems. Hence, the proposed prefetching scheme performs in an operating unit of SSD. To complement a weak point of the prefetching scheme, the proposed memory management scheme adaptively evicts uselessly prefetched data to maximize the sum of cache hit rate and prefetch hit rate. We implemented the proposed schemes as a Linux kernel module and evaluated them using a commercial SSD. The schemes improved the I/O performance up to 26% in a given experiment.

• Journal of Internet Computing and Services
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• v.16 no.5
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• pp.19-27
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• 2015

Due to the advantages of fast read/write operation and low power consumption, SSD(Solid State Drive) is now widely adopted as storage device of smart phone, laptop computer, server, etc. However, the shortcomings of SSD such as limited number of write operations and asymmetric read/write operation lead to the problem of shortened life span of SSD. Therefore, the block replacement policy of SSD used as cache for HDD is very important. The existing solutions for improving the lifespan of SSD including the LARC scheme typically employ the LRU algorithm to manage the SSD blocks, which may increase the miss rate in SSD due to the replacement of frequently used block instead of rarely used block. In this paper we propose a novel block replacement scheme which considers the block reuse interval to effectively handle various data read/write patterns. The proposed scheme replaces the block in SSD based on the recency decided by reuse interval and age along with hit ratio. Computer simulation using workload trace files reveals that the proposed scheme consistently improves the performance and lifespan of SSD by increasing the hit ratio and decreasing the number of write operations compared to the existing schemes including LARC.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.12
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• pp.94-102
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• 2016

Recently, the I/O performance of a single node is rapidly improving due to the advent of high-performance SSD. As a result, the next-generation storage platform based on SSD has received a great deal of attention and such storage platforms are increasingly adopted to commodity servers or data centers that look for the high-bandwidth computation and I/O. However, building all SSD-based storage platform may not be cost-effective because the price per storage capacity is very high as compared to that of HDD. In this paper. we propose a hybrid file management solution, called HyPLVM(Hybrid Priority Logical Volume Manager), which combines the strength of SSD with the desirable aspects of low-price, high-storage capacity HDD. HyPLVM prioritizes the files and directories to be accessed by users, in order to determine the target storage device (SSD/HDD) in which files are allocated, while mitigating the cost of building storage platforms.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.12
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• pp.57-64
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• 2008

In this paper, we propose a system-level simulator for the performance analysis of a Solid-State Disk (SSD) in PC environment by using TLM (Transaction Level Modeling) method. Our method provides quantitative analysis for a variety of architectural choices of PC system as well as SSD. Also, it drastically reduces the analysis time compared to the conventional RTL (Register Transfer Level) modeling method. To show the effectiveness of the proposed simulator, we performed several explorations of PC architecture as well as SSD. More specifically, we measured the performance impact of the hit rate of a cache buffer which temporarily stores the data from PC. Also, we analyzed the performance variation of SSD for various NAND Flash memories which show different response time with our simulator. These experimental results show that our simulator can be effectively utilized for the architecture exploration of SSD as well as PC.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06b
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• pp.462-465
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• 2011

낸드 플래시 메모리를 이용한 SSD(Solid-State Disk)는 빠른 속도와 저전력, 휴대성, 내구성 등의 특성을 가져 전통적인 저장 장치인 하드 디스크(HDD:Hard Disk Drive)를 대체할 차세대 저장 장치로 주목받고 있다. 그러나 저장 장치 성능 측정 도구는 기존의 하드 디스크의 특성을 기반으로 한 것들이 대부분으로 이를 통해 SSD의 성능을 측정하기엔 적합하지 않다. 특히 SSD는 하드 디스크에 비해 단위 공간 당비용이 수십 배 가량 높아 저장 공간의 효율적인 관리를 위해 컨트롤러(Controller)가 데이터 압축 기법을 사용하기도 하는데 이 압축 기법을 사용하는 컨트롤러에 따라 SSD는 다른 성능을 보인다. 또, 여러 가지 명령들이 한꺼번에 존재할 때 컨트롤러에 따라 이를 적절히 효율적으로 처리해주는 기능을 가지고 있는데 이 역시 SSD의 성능에 차이를 가져온다. 그러나 기존 저장 장치 성능 측정 도구는 압축 기법 유무를 판별할 수 있으면서 여러 명령들이 한꺼번에 존재할 때 SSD 성능의 차이를 파악할 수 있는 통합된 성능 측정 도구는 없다. 본 논문에서는 다양한 패턴에 따라 SSD의 특성을 측정할 수 있는 도구인 uFlip 성능 측정 도구를 기반으로, 압축 기법의 사용 유무를 판별할 수 있는 기능과 명령 큐 깊이(Command Queue Depth)에 따라 성능의 차이를 판별할 수 있는 기능을 추가하였고, uFlip 기반 수정된 성능 측정 도구로 몇 가지 상용 SSD의 성능을 평가하여 비교함으로써 추가된 기능들의 유무에 따라 SSD별로 다른 성능을 보이는 것을 확인할 수 있었다.