• Communications for Statistical Applications and Methods
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• v.15 no.3
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• pp.387-402
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• 2008

In this thesis we propose a two-stage periodic inspection model for maintaining the reliability of a system in long-term storage. There are two types of tests available; a fallible test and an error-free test. The system is overhauled at detection of failure or when the storage reliability after inspection becomes less than or equal to the prespecified value. The expected cost per unit time until overhaul is derived and a procedure for minimizing the expected cost is suggested. The two-stage periodic inspection model is compared with the one-stage periodic inspection model for various parameters of the cost function when the failure time follows exponential and Weibull distributions. The proposed model is then applied to an existing missile system for comparison with the current inspection policy.

• KIPS Transactions on Computer and Communication Systems
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• v.3 no.11
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• pp.409-418
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• 2014

The amount of data located in storage servers has dramatically increased with the growth in cloud and social networking services. Storage systems with very large capacities may suffer from poor reliability and long latency, problems which can be addressed by the use of a hybrid disk, in which mechanical and flash memory storage are combined. The Linux-based SSD(solid-state disk) uses a caching technique based on the DM-cache utility. We assess the limitations of DM-cache by evaluating its performance in diverse environments, and identify problems with the caching policy that it operates in response to various commands. This policy is effective in reducing latency when Linux is running in native mode; but when Linux is installed as a guest operating systems on a virtual machine, the overhead incurred by caching actually reduces performance.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.6
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• pp.1299-1306
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• 2023

In this paper, we present a system for undesignated cultural heritage management and real-time theft chase, which uses flash-based large-capacity storage. The proposed system is composed of 3 parts, such as a cultural management device, a flash-based server, and a monitoring service for managing cultural heritages and chasing thefts using IoT technologies. However flash-based storage needs methods to overcome the limited lifespan. Therefore, in this paper, we present a system, which uses the disk buffer in flash-based storage to overcome the disadvantage, and evaluate the system performance in various environments. In our experiments, LRU policy shows the number of direct writes in the flash-based storage by 10.7% on average compared with CLOCK and FCFS.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.5
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• pp.546-553
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• 2015

Recently, flash cache is widely adopted as the performance accelerator of legacy storage systems. Unlike other cache media, flash cache should be carefully managed as it has peculiar characteristics such as long write latency and limited P/E cycles. In particular, we make two prominent observations that can be utilized in managing flash cache. First, a serious worn-out problem happens when the working-set of a system is beyond the capacity of flash cache due to excessively frequent cache replacement. Second, more than 50% of data has no hit in flash cache as it is a second level cache. Based on these observations, we propose a cache admission control policy that does not cache data when it is first accessed, and inserts it into the cache only after its second access occurs within a certain time window. This allows the filtering of data disruptive to flash cache in terms of endurance and performance. With this policy, we prolong the lifetime of flash cache 2.3 times without any performance degradations.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.562-574
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• 2023

Carbon neutrality has been suggested to overcome the global climate crisis caused by global climate change. Hydrogen energy is a major way to achieve carbon neutrality, and the developments and policies of hydrogen technology have been proposed to achieve this goal. To commercialize hydrogen energy resources, it is necessary to understand the overall value chain composed of hydrogen production, storage, and utilization and to present the direction of technological developments. In this paper the hydrogen strategies of major countries, including Europe, the United States, Japan, China, and South Korea will be analyzed, and hydrogen technologies by value chain will also be explain. This paper will contribute to understanding the overall hydrogen policy and technology, as both policy and technology are summarized.

• International Journal of Computer Science & Network Security
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• v.22 no.3
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• pp.364-374
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• 2022

Health information systems (HIS) are facing security challenges on data privacy and confidentiality. These challenges are based on centralized system architecture creating a target for malicious attacks. Blockchain technology has emerged as a trending technology with the potential to improve data security. Despite the effectiveness of this technology, still HIS are suffering from a lack of data privacy and confidentiality. This paper presents a blockchain-based data storage security architecture integrated with an e-Health care system to improve its security. The study employed a qualitative research method where data were collected using interviews and document analysis. Execute-order-validate Fabric's storage security architecture was implemented through private data collection, which is the combination of the actual private data stored in a private state, and a hash of that private data to guarantee data privacy. The key findings of this research show that data privacy and confidentiality are attained through a private data policy. Network peers are decentralized with blockchain only for hash storage to avoid storage challenges. Cost-effectiveness is achieved through data storage within a database of a Hyperledger Fabric. The overall performance of Fabric is higher than Ethereum. Ethereum's low performance is due to its execute-validate architecture which has high computation power with transaction inconsistencies. E-Health care system administrators should be trained and engaged with blockchain architectural designs for health data storage security. Health policymakers should be aware of blockchain technology and make use of the findings. The scientific contribution of this study is based on; cost-effectiveness of secured data storage, the use of hashes of network data stored in each node, and low energy consumption of Fabric leading to high performance.

• Journal of KIISE:Computing Practices and Letters
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• v.13 no.6
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• pp.422-426
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• 2007

Personal mobile devices equipped with non-volatile storage such as MP3 player, PMP, cellular phone, and USB memory require safety for the stored data on the devices. One of the safety requirements is secure deletion, which is removing stored data completely so that the data can not be restored illegally. In this paper, we study how to design the secure deletion on Flash memory, commonly used as storage media for mobile devices. We consider two possible secure deletion policy, named zero-overwrite and garbage-collection respectively, and analyze how each policy affects the performance of Flash memory file systems. Then, we propose an adaptive file deletion scheme that exploits the merits of the two possible policies. Specifically, the proposed scheme applies the zero-overwrite policy for small files, whereas it employs the garbage-collection policy for large files. Real implementation experiments show that the scheme is not only secure but also efficient.

• The Journal of the Korea Contents Association
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• v.8 no.11
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• pp.57-64
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• 2008

The data grid computing provides geographically distributed storage resources to solve computational problems with large-scale data. Unlike cache replacement policies in virtual memory or web-caching replacement, an optimal file replacement policy for data grids is the one of the important problems by the fact that file size is very large. The traditional file replacement policies such as LRU(Least Recently Used), LCB-K(Least Cost Beneficial based on K), EBR(Economic-based cache replacement), LVCT(Least Value-based on Caching Time) have the problem that they have to predict requests or need additional resources to file replacement. To solve theses problems, this paper propose SBR-k(Sized-based replacement-k) that replaces files based on file size. The proposed policy considers file size to reduce the number of files corresponding to a requested file rather than forecasting the uncertain future for replacement. The results of the simulation show that hit ratio was similar when the cache size was small, but the proposed policy was superior to traditional policies when the cache size was large.

• Journal of Climate Change Research
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• v.7 no.3
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• pp.237-247
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• 2016

Global warming caused by greenhouse gases is one of the foremost challenges in the international community. As an alternative to solve this problem, the importance of CCS (Carbon Capture and Storage) technology is increasing. However, due to the delay of European financial crisis recovery, some large-scale CCS projects were postponed. In turn, large-scale CCS projects in South Korea have not been launched as originally planned. Given these situations, it is important to review the latest R&D activities related to CCS in South Korea, and then adjust relevant national policy accordingly. The purpose of this study is to identify policy issues for the effective promotion of CCS technology in South Korea. Following the analysis of recent global trend on CCS policy, we evaluated the results and achievements from national CCS projects, which had been listed under the "Korean National CCS Master Action Plan (2010)". Especially, we tried to review the attainability for the original goal of each project. Through the present study, we identified the current status of CCS technology in South Korea and suggested efficient ways to be taken in order to increase efficiency in implementing national CCS policy in the future.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10a
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• pp.89-91
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• 1998

현대 사회의 정보 요구 증가와 편리함의 추구는 정보통신 기술의 발달과 함께 멀티미디어 데이터 서비스를 급증 시켰다. NOD 데이터의 경우 이러한 요구에 부합하므로, 많은 사용자를 가지게 될 것이며, 그에 따른 제반 요건으로 서버 구현에서 scalability, availability, reliability 등이 중요한 요건이다. 따라서 이러한 요건을 멀티미디어 데이터 특성을 이용한 저장 방법으로 만족시키려는 많은 연구가 있다. 그러나 NOD 시스템에 대한 연구는 미흡한 실정이며 clustered 환경에서의 New 데이터에 대한 연구는 거의 없다. VOD 데이터에 적합한 것으로 알려진 일반적인 저장 방법이 NOD 데이터에 반드시 적합한 것이 아니며, 본 논문에서는 기존에 연구된 데이터 저장 방법 중에서 NOD 데이터의 small volume, skewed popularity distribution 등의 특성을 고려하여 clustered storage server환경에 맞는 striping 정책을 찾는다.