• The Journal of Korean Association of Computer Education
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• v.18 no.2
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• pp.83-90
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• 2015

In an virtualization environment, several virtual machines use physical resources together. If a specific virtual machine uses to much of the computing resources, other machines may not be working properly. There are various method to solve this problem. Most representative study is to migrate a specified virtual machines to a different server, a target server. In this study, server load can be transferred to a target server by the remigrate of the load imposed on virtual machine. It is still problematic that virtual machine has to remigrate to a different server. This thesis has proposed the algorithm determining the remigration targets by applying dynamic thresholds to solve those problems. The migration algorithm applies dynamic thresholds according to the following criteria. Firstly, the usage of CPU, network and memory; secondly, decide the set of artificial machine and the target server based on the resources surpassed thresholds; thirdly, determine artificial machines based on the resource usage in the target server.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.52-55
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• 2014

가상화 환경에서 물리 서버 자원의 효율적인 사용을 위하여 부하가 많은 물리 서버로부터 부하가 적은 물리 서버로 가상 머신을 옮기는 실시간 이주 기법은 많은 네트워크 대역폭을 사용하게 된다. 이로 인해 물리 서버의 가용 네트워크 대역폭이 감소하여 다른 가상 머신들의 네트워크 성능 저하를 불러일으킨다. 본 논문에서는 이러한 문제를 해결하고자 전송되는 페이지들의 값들을 비교하며, 특정 값으로만 이루어진 페이지들을 전송하지 않는 가상 머신 이주 기법을 제안한다.

• Proceedings of the Korean Society of Computer Information Conference
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• 2012.01a
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• pp.5-6
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• 2012

본 논문에서는 가상머신에서 수행되는 어플리케이션의 서비스 품질을 보장하고, 클라우드 클러스터의 운영비용을 절감시킬 수 있는 자원 할당 감축기법을 제안한다. 이 기법은 가상머신의 자원 사용량 변화 추세를 분석하고 이를 토대로 확률적인 접근을 사용하여 새로운 자원 할당 감축량을 결정한다. 가상머신의 자원 사용량이 할당량을 초과하면 가상머신의 이주가 필요하다. 이때 발생하는 다운타임동안 가상머신의 어플리케이션은 서비스를 수행할 수 없기 때문에 클라우드 시스템의 성능이 저하된다. 따라서 성능평가에서는 가상머신의 자원 사용량이 할당량을 초과하는 횟수를 측정하여 Greedy 기법과 비교 평가함으로써 제안한 기법이 자원 할당 감축에 우수함을 검증한다.

• KIISE Transactions on Computing Practices
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• v.22 no.6
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• pp.278-283
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• 2016

Due to explosive increase in the amount of data produced recently, cloud storage system is required to offer high and stable performance. However, VM (Virtual Machine) migration may result in lowered storage service performance. Especially, in an environment where the host-side flash cache is used in a cloud system, the existing warmed up cache is lost and the problematic cold start begins at a new cache due to a VM migration. In this paper, we first demonstrate and analyze the cold start problem and then propose Cachemior (Cache migrator) which enables efficient hot start of the flash cache.

• Journal of Internet Computing and Services
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• v.18 no.4
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• pp.51-59
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• 2017

With the growth of Cloud computing, it is important to consider resource management techniques to minimize the overall costs of management. In cloud environments, each host's utilization and virtual machine's request based on user preferences are dynamic in nature. To solve this problem, efficient allocation method of virtual machines to hosts where the classification of virtual machines and hosts is undetermined should be studied. In reducing the number of active hosts to reduce energy consumption, thresholds can be implemented to migrate VMs to other hosts. By using Fuzzy logic in classifying resource requests of virtual machines and resource utilization of hosts, we proposed an adaptive VM allocation and migration approach. The allocation strategy classifies the VMs according to their resource request, then assigns it to the host with the lowest resource utilization. In migrating VMs from overutilized hosts, the resource utilization of each host was used to create an upper threshold. In selecting candidate VMs for migration, virtual machines that contributed to the high resource utilization in the host were chosen to be migrated. We evaluated our work through simulations and results show that our approach was significantly better compared to other VM allocation and Migration strategies.

• Proceedings of the Korea Information Processing Society Conference
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• 2018.05a
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• pp.256-259
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• 2018

다수의 사용자가 자원을 공유하는 클라우드 센터에서는 자원 사용량 예측이 힘들기 때문에 지속적으로 가상머신의 자원 부족과 특정 물리 서버에 가상머신들이 집중되는 것을 방지하고자 클라우드 센터를 구성하는 다수의 물리 서버 사이에서 가상머신을 이주시키는 마이그레이션 작업을 수행한다. 가상머신 마이그레이션은 가상머신에게 할당된 자원의 규모에 따라 물리 서버에 가상머신을 균등하게 배치시킬 수 있지만 가상머신의 특정 자원에 따른 자원 집중 현상은 방지할 수 없다. 본 논문에서는 가상머신 마이그레이션 작업 시 자원 집중 현상을 방지하기 위한 기반 정보를 생성하는 가상머신 유형분류 기법을 제안한다. 본 논문에서 제안하는 가상머신 유형분류 기법은 물리 서버에서 실행 중인 가상머신의 자원 사용 정보를 기반으로 CPU, 메모리 유형으로 분류하여 가상머신 마이그레이션을 수행할 때 사용할 수 있는 기반 정보를 제공한다. 또한 본 논문에서 제안한 기법은 실험을 통해 무시할 수 있는 수준의 오버헤드를 발생시키는 것을 확인하였다.

• Proceedings of the Korean Society of Computer Information Conference
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• 2011.06a
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• pp.15-16
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• 2011

본 논문에서는 클라우드 컴퓨팅 환경에서 저장공간 이주(storage migration)시에 저장공간의 읽기/쓰기 비율을 고려한 저장공간 복제 모델 선정을 위한 실험 환경을 설계한다. 기존의 저장공간 이주 모델은 가상머신과 저장공간중에 저장공간이 먼저 이주하는 선복제(pre-copy)와 나중에 이주하는 후복제(post-copy)가 있다. 이러한 복제 기법은 VM과 저장공간 이주의 필요성과 그 방법만을 제안하였으며, 성능 향상을 위한 이주 기법 선정 방법은 제시하지 못하였다. 따라서 본 논문에서는 클라우드 컴퓨팅 환경에서 다양한 스토리지의 읽기/쓰기 비율에 따른 이주 모델 선정 기법을 실험할 수 있는 시뮬레이터 설계 방법을 제시한다.

• Journal of the Korea Society of Computer and Information
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• v.19 no.11
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• pp.1-7
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• 2014

In this paper, we propose a virtual machine(VM) remapping scheme that reduces VM relocation time on a cloud cluster. The proposed scheme finds VMs that should be migrated in sequence from a given VM map, and exchanges destinations of some VMs among them to reduce the VM relocation time. The VMs, the destinations of which will be exchanged, are chosen based on the amount of physical machine's available resources and migration completion time. The exchange of destinations is repeated until the VM relocation time cannot be shortened any further. Through a simulation, we show that the proposed scheme reduces VM relocation time by 42.7% in maximum.

• Journal of the Korea Society of Computer and Information
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• v.17 no.5
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• pp.1-7
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• 2012

In this paper, we design and implement the simulator for WAN storage replication model performance evaluation in cloud computing environment. Each cloud of simulator is composed of virtual machine emulator and storage emulator. The virtual machine emulator is composed of read/write ratio module, the read/write sequence combination module, and the read/write request module. The storage emulator is composed of storage management module, data transfer module, read/write operations module, and overhead processing module. Using the simulator, we evaluate performance of migration scheme, pre-copy and the post-copy, considering about read/write ratio, network delay, and network bandwidth. Through simulation, we have confirmed that the average migration time of pre-copy was decreased proportional to the read operation. However, average migration time of post-copy was on the increase. Also, the average migration time of post-copy was increased proportional to the network delay. However, average migration time of pre-copy was shown uniformly. Therefore, we show that pre-copy model more effective to reduce the average migration time than the post-copy model. The average migration time of pre-copy and post-copy were not affected by the change of network bandwidth. Therefore, these results show that selects the storage replication model to be, the network bandwidth know not being the important element.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.8
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• pp.868-872
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• 2010

Many embedded Java systems are equipped with limited memory, which can constrain the code cache size provided for Java just-in-time compilation, affecting the Java performance. This paper proposes expanding the limited code cache when it is full, by saving the machine code for some methods in the code cache into the file system of the permanent storage and reloading it to the code cache when they are re-invoked later. This is applying the client ahead-of-time compilation during the execution time for the purpose of enlarging the code cache. Our experimental results indicate that the proposed execution method can improve the performance by as much as 1.6 times compared to the conventional method, when the code cache size is reduced by half.