• The Journal of Society for e-Business Studies
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• v.15 no.4
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• pp.101-121
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• 2010

This paper presents an intelligent prefetching technique that significantly improves performance of hybrid fash-disk storage, a combination of flash memory and hard disk. Since flash memory embedded in a hybrid device is much faster than hard disk in terms of I/O operations, it can be utilized as a 'cache' space to improve system performance. The basic strategy for prefetching is to utilize sequential pattern mining, with which we can extract the access patterns of objects from historical access sequences. We use two techniques for enhancing the performance of hybrid storage with prefetching. One of them is to modify a FAST algorithm for mapping the flash memory. The other is to extend the unit of prefetching to a block level as well as a file level for effectively utilizing flash memory space. For evaluating the proposed technique, we perform the experiments using the synthetic data and real UCC data, and prove the usability of our technique.

• International Journal of Internet, Broadcasting and Communication
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• v.10 no.3
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• pp.26-34
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• 2018

In this paper, we propose a scheduling scheme that can efficiently serve I/O requests having deadlines in flash storage. The I/O requests with deadlines, namely, real-time requests, are assumed to be issued for streaming services of continuous media. Since a Web-based streaming server commonly supports downloads of HTMLs or images, we also aim to quickly process non-real-time I/O requests, together with real-time ones. For this purpose, we adopt the well-known rate-reservation EDF (RR-EDF) algorithm for determining scheduling priorities among mixed I/O requests. In fact, for the use of an EDF-style algorithm, overhead of task's switching should be low and predictable, as with its application of CPU scheduling. In other words, the EDF algorithm is inherently unsuitable for scheduling I/O requests in HDD storage because of highly varying latency times of HDD. Unlike HDD, time for reading a block in flash storage is almost uniform with respect to its physical location. This is because flash storage has no mechanical component, differently from HDD. By capitalizing on this uniform block read time, we compute bandwidth utilization rates of real-time requests from streams. Then, the RR-EDF algorithm is applied for determining how much storage bandwidth can be assigned to non-real-time requests, while meeting deadlines of real-time requests. From this, we can improve the service times of non-real-time requests, which are issued for downloads of static files. Because the proposed scheme can expand flexibly the scheduling periods of streams, it can provide a full usage of slack times, thereby improving the overall throughput of flash storage significantly.

• Journal of the Korea Society of Computer and Information
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• v.25 no.2
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• pp.21-29
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• 2020

The use of NAND flash memory is continuously increased with the demand of mobile data in the IT industry environment. However, the erase operations in flash memory require longer latency and higher power consumption, resulting in the limited lifetime for each cell. Therefore, frequent write/erase operations reduce the performance and the lifetime of the flash memory. In order to solve this problem, management techniques for improving the performance of flash based storage by reducing write and erase operations of flash memory with using disk buffers have been studied. In this paper, we propose a CPWL to minimized the number of write operations. It is a disk buffer management that separates read and write pages according to the characteristics of the buffer memory access patterns. This technique increases the lifespan of the flash memory and decreases an energy consumption by reducing the number of writes by arranging pages according to the characteristics of buffer memory access mode of requested pages.

• Journal of the Korean Institute of Gas
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• v.19 no.4
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• pp.8-14
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• 2015

For the safe handling of 2-methyl-1-butanol being used in various ways in the chemical industry, the flash point and the autoignition temperature(AIT) of 2-methyl-1-butanol was experimented. And, the lower explosion limit of 2-methyl-1-butanol was calculated by using the lower flash point obtained in the experiment. The flash points of 2-methyl-1-butanol by using the Setaflash and Pensky-Martens closed-cup testers measured $40^{\circ}C$ and $44^{\circ}C$, respectively. The flash points of 2-methyl-1-butanol by using the Tag and Cleveland open cup testers are measured $49^{\circ}C$ and $47^{\circ}C$. The AIT of 2-methyl-1-butanol by ASTM 659E tester was measured as $335^{\circ}C$. The lower explosion limit by the measured flash point $40^{\circ}C$ was calculated as 1.30 Vol.%. It was possible to predict lower explosion limit by using the experimental flash point or flash point in the literature.

• Journal of the Korean Institute of Gas
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• v.12 no.3
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• pp.50-55
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• 2008

The flash points for the systems, ethlybenzene+n-butanol and ethlybenzene+n-hexanol, were measured by using Tag open-cup tester (ASTM D1310-86). These binary mixtures exhibited MFPB (minimum flash point behavior), which leads to the minimum on the flash point vs composition curve. The experimental data were compared with the values calculated by the Raoult's law, the UNIQUAC equation and the NRTL equation. The calculated values based on the UNIQUAC and NRTL equations were found to be better than those based on the Raoult's law. It was concluded that the UNIQUAC and NRTL equations were more effective than the Raoult' law at describing the activity coefficients for nonideal solution such as the ethlybenzene+n-butanol and ethlybenzene+n-hexanol systems. And the predictive curve of the flash point prediction model based on the NRTL equation described the experimentally-derived data more effectively than was the case when the prediction model was based upon the UNIQUAC equation.

• 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.

• Journal of the Korean Society of Safety
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• v.22 no.4
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• pp.37-42
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• 2007

Flash points for the flammable binary systems, n-propanol+acetic acid and n-propanol+n-propionic acid, were measured by Cleveland open cup tester. The Raoult's law, the van Laar equation and the UNIQUAC equation were used for predicting flash points and were compared with experimentally-derived data. The calculated values based on the van Laar and UNIQUAC equations were found to be better than those based on the Raoult's law. And the predictive curve of the flash point prediction model based on the UNIQUAC equation described the experimentally-derived data more effectively than was the case when the prediction model was based upon the the van Laar equation.

• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.566-571
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• 2014

Channel-stacked 3D NAND flash memory is very promising candidate for the next-generation NAND flash memory. However, there is an inherent issue on cell size variation between stacked channels due to the declined etch slope. In this paper, the effect of the cell variation on the incremental step pulse programming (ISPP) characteristics is studied with 3D TCAD simulation. The ISPP slope degradation of elliptical channel is investigated. To solve that problem, a new programming method is proposed, and we can alleviate the $V_T$ variation among cells and reduce the total programming time.

• Journal of Korean Association for Spatial Structures
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• v.16 no.3
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• pp.89-97
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• 2016

With the recent trend to construct high-rise and large buildings, the steel structure system is widely used, but there are not enough studies on the vibration characteristics of the iFLASH system on the buildings. Therefore, in this study, we performed a vibration measurement of the natural frequency and damping ratio in the stage of iFLASH panel, composit, frame completion and cladding completion. The result findings suggest that the damping ratio after the cladding completion has a greater effect on the reduction of the damping ratio, than the stage after the frame completion.

• Journal of Welding and Joining
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• v.25 no.2
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• pp.55-61
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• 2007

Flash butt weldability of 590MPa dual phase steel is carried out under micro metallographical examination and macro mechanical property tests. The objective of present study is to investigate the cause that brings on bond line fracture, and is to improve mechanical properties of the flash butt welded joint. The joint of flash butt welding has a superior tensile property, but has bad formability due to oxide formed at bond interface. The HAZ softening in the weld joint does not show. It was found that mechanical properties were increased with optimizing welding parameters and making application of oil dripping and post-weld heat treatment.