• KIPS Transactions on Computer and Communication Systems
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• v.5 no.11
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• pp.379-384
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• 2016

NAND flash storage is widely used for computer systems, because of it has faster response time, lower power consumption, and larger capacity per unit area than hard disk. However, currently used I/O scheduler in the operating system is optimized for characteristics of the hard disk. Therefore, the conventional I/O scheduler includes the unnecessary overhead in the case of the NAND flash storage to be applied. Particularly, when the write requests performed intensively, garbage collection is performed intensively. So, it occurs the problem that the processing of the I/O request delay. In this paper, we propose the new I/O scheduler to solve the problem of garbage collection performs intensively, and to optimize for NAND flash storage. In the result of performance evaluation, proposed scheme shows an improvement the user responsiveness by reducing 1% of the average read response time and 78% of the maximum response time.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.9
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• pp.54-62
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• 2015

Although NAND flash-based SSD (Solid-State Drive) provides superior performance in comparison to HDD (Hard Disk Drive), it has a major drawback in write endurance. As a result, the lifetime of SSD is determined by the workload and thus it becomes a big challenge in current technology trend of such as the shifting from SLC (Single Level Cell) to MLC (Multi Level cell) and even TLC (Triple Level Cell). Most previous studies have dealt with wear-leveling or improving SSD lifetime regarding hardware architecture. In this paper, we propose the optimal configuration of host I/O stack focusing on file system, I/O scheduler, and link power management using JEDEC enterprise workloads in terms of WAF (Write Amplification Factor) which represents the efficiency perspective of SSD life time especially for host write processing into flash memory. Experimental analysis shows that the optimum configuration of I/O stack for the perspective of SSD lifetime is MinPower-Dead-XFS which prolongs the lifetime of SSD approximately 2.6 times in comparison with MaxPower-Cfq-Ext4, the best performance combination. Though the performance was reduced by 13%, this contributions demonstrates a considerable aspect of SSD lifetime in relation to I/O stack optimization.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.1599-1602
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• 2012

스마트폰이나 태블릿PC와 같은 모바일기기 보급의 확산으로 모바일 클라우드 컴퓨팅이 발전하고 있다. 이와 같은 클라우드 컴퓨팅의 핵심 기술은 가상화 기술이며 서버 가상화가 근간을 이룬다. 가상 서버는 물리 서버의 성능 이상을 추구하고 있으며 디스크 I/O에 따라 성능이 크게 좌우된다. 본 논문에서는 가상 서버 상에서 NAS, Local SAS, PCI-SSD와 같은 다양한 디스크에 대한 I/O 성능을 테스트하였고, 이를 근거로 디스크 I/O 성능에 따른 가상 서버 통합에 대해 고찰하였다.

• International journal of advanced smart convergence
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• v.1 no.2
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• pp.26-29
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• 2012

Recently, to efficiently support the real-time requirements of RTLS( Real Time Location System) services, interest in the main memory DBMS is rising. In the main memory DBMS, because all data can be lost when the system failure happens, the recovery method is very important for the stability of the database. Especially, disk I/O in executing the log and the checkpoint becomes the bottleneck of letting down the total system performance. Therefore, it is urgently necessary to research about the recovery method to reduce disk I/O in the main memory DBMS. Therefore, In this paper, we analyzed existing log techniques and check point techniques and existing main memory DBMSs' recovery techniques for recovery techniques research for main memory DBMS.

• Journal of the Korea Society for Simulation
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• v.1 no.1
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• pp.87-102
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• 1992

This paper presents the development of event-driven system level simulation tool SMPLE(Smpl Extende, an extention fo smpl) and its application to the performance analysis of multiprocessor computer systems. Because of its data structure, it is very difficult to change, expand or add new functions to simulation language smpl implemented by MacDougall. In SMPLE, we change data structure with structure and pointer, add new functions, and enable dynamic memory management. Using new data structure, facilities, and functions added in SMPLE, we simulate job processing of a shared bus multiprocessor system with autonomous hierarchical I/O subsystem. We set system performance contribution of subsystems and units. The impact of disk I/O on system performance is evaluated under vairous conditions of number of processors, processing power, memory access time and disk seek time.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.11a
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• pp.531-534
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• 2007

우리는 이 논문에서 현대 마그네틱 디스크 드라이브를 대상으로 하여 내부의 세부적인 동작 메커니즘을 상위 레벨의 검침 프로그램을 이용하여 정확하게 측정하고 이를 통해서 디스크 드라이브를 사용하는 다양한 응용 프로그램 및 운영 체제 시스템의 디스크 입/출력 성능을 개선하고자 한다.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.35C no.3
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• pp.46-58
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• 1998

Multi-disk data allocation problem examined in this paper is to find a method to distribute a Binary Cartesian Product File on multiple disks to maximize parallel disk I/O accesses for partial match retrieval. This problem is known to be NP-hard, and heuristkc approaches have been applied to obtain sub-optimal solutions. Recently, efficient methods have been proposed with a restriction that the number of disks in which files are stored should be power of 2. In this paper, we propose a new disk Allocation method based on Genetic Algorithm(GA) to remove the restriction on the number of disks to be applied. Using the schema theory, we prove that our method can find a near-optimal solutionwith high probability. We compare the quality of solution derived by our method with General Disk Modulo, Binary Disk Modulo, and Error Correcting Code methods through the simulation. The simulation results show that proposed GA is superior to GDM method in all cases and provides comparable performance to the BDM method which has a restriction on the number of disks.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.41 no.2
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• pp.9-22
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• 2004

This paper presents a parallel genetic algorithm for the Multi-disk data allocation problem an NP-complete problem. This problem is to find a method to distribute a Binary Cartesian Product File on disk-arrays to maximize parallel disk I/O accesses. A Sequential Genetic Algorithm(SGA), DAGA, has been proposed and showed the superiority to the other proposed methods, but it has been observed that DAGA consumes considerably lengthy simulation time. In this paper, a parallel version of DAGA(ParaDAGA) is proposed. The ParaDAGA is a 2-dimension torus-based Parallel Genetic Algorithm(PGA) and it is based on a distributed population structure. The ParaDAGA has been implemented on the parallel computer simulated on a single processor platform. Through the simulation, we study the impact of varying ParaDAGA parameters and compare the quality of solution derived by ParaDAGA and DAGA. Comparing the quality of solutions, ParaDAGA is superior to DAGA in all cases of configurations in less simulation time.

• The KIPS Transactions:PartA
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• v.11A no.7 s.91
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• pp.547-554
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• 2004

To play back CM (Continuous Media) in online mode, the multimedia system Is required to have a real-time disk scheduling scheme that can efficiently fulfill the strict temporal constraints of serviced CM streams to prevent hiccups. In general, such disk scheduling is performed based on the concept of periodic prefetching since a CM stream has a rather long Playback time. In this paper, we also propose a periodic prefetching scheme that runs by using real-time disk channels, called on-time delivery channels. Since the channels are generated from the bulk-SCAN algorithm and they can be allocated in a very flexible manner based on the EDF (earliest-deadline-first) algorithm, the proposed scheme provides a better Performance in terms of I/O throughput and the average response time, as well as hiccup-free playback of concurrent CM streams. To show that the proposed scheme outperforms other methods, we give some simulation results.

• The KIPS Transactions:PartA
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• v.8A no.4
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• pp.375-384
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• 2001

The shared disk file systems use a technique known as file system journaling to support recovery of metadata on the SAN(Storage Area Network). In the existing journaling technique, the metadata that is dirtied by one host must be updated to disk space before some hosts access it. The system performance is decreased because the disk access number is increased. In this paper, we describe a new recovery technique using a global buffer to decrease disk I/O. It transmits the dirtied metadata into the other hosts through Fibre Channel network on the SAN instead of disk I/O and supports recovery of a critical data by journaling a data as well as metadata.