The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Jaehyuk Huh - One of the best experts on this subject based on the ideXlab platform.
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vcache architectural support for transparent and isolated virtual llcs in Virtualized environments
International Symposium on Microarchitecture, 2015Co-Authors: Daehoon Kim, Hwanju Kim, Nam Sung Kim, Jaehyuk HuhAbstract:A key role of virtualization is to give an illusion that a consolidated workload runs on a dedicated machine although the underlying resources are actively shared by multiple workloads. Technical advances have enabled a virtual machine (VM) to exercise many shared resources of a machine in a transparent and isolated manner. However, such an illusion of resource dedication has not been supported for the last-level cache (LLC), although the LLC is the largest on-chip shared resource with a significant performance impact. In this paper, we propose vCache--architectural support to provide a transparent and isolated virtual LLC (vLLC) for each VM and interfaces to manage the vLLC. More specifically, this study first proposes architectural support for the guest OS of a VM to index the LLC with its guest physical address instead of a host physical address. This in turn allows that the guest OS transparently view its vLLC and preserve the effectiveness of its page placement policy. Second, this study extends the architectural support for each VM to keep its vLLC strongly isolated from other VMs. Such resource dedication is critical to offer performance isolation and preserve vLLC transparency for each VM in a highly consolidated machine. With little hardware overhead, vCache can facilitate various unchartered vLLC capacity-based services for the public clouds while providing up to 17% higher performance than a traditional Virtualized System.
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MICRO - vCache: architectural support for transparent and isolated virtual LLCs in Virtualized environments
Proceedings of the 48th International Symposium on Microarchitecture, 2015Co-Authors: Daehoon Kim, Hwanju Kim, Nam Sung Kim, Jaehyuk HuhAbstract:A key role of virtualization is to give an illusion that a consolidated workload runs on a dedicated machine although the underlying resources are actively shared by multiple workloads. Technical advances have enabled a virtual machine (VM) to exercise many shared resources of a machine in a transparent and isolated manner. However, such an illusion of resource dedication has not been supported for the last-level cache (LLC), although the LLC is the largest on-chip shared resource with a significant performance impact. In this paper, we propose vCache--architectural support to provide a transparent and isolated virtual LLC (vLLC) for each VM and interfaces to manage the vLLC. More specifically, this study first proposes architectural support for the guest OS of a VM to index the LLC with its guest physical address instead of a host physical address. This in turn allows that the guest OS transparently view its vLLC and preserve the effectiveness of its page placement policy. Second, this study extends the architectural support for each VM to keep its vLLC strongly isolated from other VMs. Such resource dedication is critical to offer performance isolation and preserve vLLC transparency for each VM in a highly consolidated machine. With little hardware overhead, vCache can facilitate various unchartered vLLC capacity-based services for the public clouds while providing up to 17% higher performance than a traditional Virtualized System.
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architectural support for secure virtualization under a vulnerable hypervisor
International Symposium on Microarchitecture, 2011Co-Authors: Seongwook Jin, Jeongseob Ahn, Sanghoon Cha, Jaehyuk HuhAbstract:Although cloud computing has emerged as a promising future computing model, security concerns due to malicious tenants have been deterring its fast adoption. In cloud computing, multiple tenants may share physical Systems by using virtualization techniques. In such a Virtualized System, a software hypervisor creates virtual machines (VMs) from the physical System, and provides each user with an isolated VM. However, the hypervisor, with a full control over hardware resources, can access the memory pages of guest VMs without any restriction. By compromising the hypervisor, a malicious user can access the memory contents of the VMs used by other users. In this paper, we propose a hardware-based mechanism to protect the memory of guest VMs from unauthorized accesses, even with an untrusted hypervisor. With this mechanism, memory isolation is provided by the secure hardware, which is much less vulnerable than the software hypervisor. The proposed mechanism extends the current hardware support for memory virtualization with a small extra hardware cost. The hypervisor can still flexibly allocate physical memory pages to virtual machines for efficient resource management. However, the hypervisor can update nested page tables only through the secure hardware mechanism, which verifies each mapping change. Using the hardware-oriented mechanism in each System securing guest VMs under a vulnerable hypervisor, this paper also proposes a cloud System architecture, which supports the authenticated launch and migration of guest VMs.
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MICRO - Architectural support for secure virtualization under a vulnerable hypervisor
Proceedings of the 44th Annual IEEE ACM International Symposium on Microarchitecture - MICRO-44 '11, 2011Co-Authors: Seongwook Jin, Jeongseob Ahn, Sanghoon Cha, Jaehyuk HuhAbstract:Although cloud computing has emerged as a promising future computing model, security concerns due to malicious tenants have been deterring its fast adoption. In cloud computing, multiple tenants may share physical Systems by using virtualization techniques. In such a Virtualized System, a software hypervisor creates virtual machines (VMs) from the physical System, and provides each user with an isolated VM. However, the hypervisor, with a full control over hardware resources, can access the memory pages of guest VMs without any restriction. By compromising the hypervisor, a malicious user can access the memory contents of the VMs used by other users. In this paper, we propose a hardware-based mechanism to protect the memory of guest VMs from unauthorized accesses, even with an untrusted hypervisor. With this mechanism, memory isolation is provided by the secure hardware, which is much less vulnerable than the software hypervisor. The proposed mechanism extends the current hardware support for memory virtualization with a small extra hardware cost. The hypervisor can still flexibly allocate physical memory pages to virtual machines for efficient resource management. However, the hypervisor can update nested page tables only through the secure hardware mechanism, which verifies each mapping change. Using the hardware-oriented mechanism in each System securing guest VMs under a vulnerable hypervisor, this paper also proposes a cloud System architecture, which supports the authenticated launch and migration of guest VMs.
Kishor S. Trivedi - One of the best experts on this subject based on the ideXlab platform.
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Analyzing Software Rejuvenation Techniques in a Virtualized System: Service Provider and User Views
IEEE Access, 2020Co-Authors: Jing Bai, Kishor S. Trivedi, Fumio Machida, Xiaolin Chang, Zhen HanAbstract:Virtualization technology has promoted the fast development and deployment of cloud computing, and is now becoming an enabler of Internet of Everything. Virtual machine monitor (VMM), playing a critical role in a Virtualized System, is software and hence it suffers from software aging after a long continuous running as well as software crashes due to elusive faults. Software rejuvenation techniques can be adopted to reduce the impact of software aging. Although there existed analytical model-based approaches for evaluating software rejuvenation techniques, none analyzed both application service (AS) availability and job completion time in a Virtualized System with live virtual machine (VM) migration. This paper aims to quantitatively analyze software rejuvenation techniques from service provider and user views in a Virtualized System deploying VMM reboot and live VM migration techniques for rejuvenation, under the condition that all the aging time, failure time, VMM fixing time and live VM migration time follow general distributions. We construct an analytical model by using a semi-Markov process (SMP) and derive formulas for calculating AS availability and job completion time. By analytical experiments, we can obtain the optimal migration trigger intervals for achieving the approximate maximum AS availability and the approximate minimum job completion time, and then service providers can make decisions for maximizing the benefits of service providers and users by adjusting parameter values.
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CIT - Availability Modeling and Analysis of a Virtualized System Using Stochastic Reward Nets
2016 IEEE International Conference on Computer and Information Technology (CIT), 2016Co-Authors: Dong Seong Kim, Fumio Machida, Jin B. Hong, Tuan A.h. Nguyen, Jong Sou Park, Kishor S. TrivediAbstract:Availability is one of the key requirements for modern networked System. Availability of a Virtualized System can be modelled and analyzed using stochastic models. In our previous work, availability of a Virtualized System was modeled using a hierarchical model to incorporate the detailed behavior of virtual machines (VMs)' failure and recovery with respect to the System behavior. In particular, a truncated continuous time Markov chain model was used for VM mode. In this paper, we propose to construct a stochastic reward nets (SRN) to model and analyze the availability of a Virtualized System. Further, we study the effect on the availability when restrictions on the guard functions are relaxed. We use a Virtualized data center (VDC) using three hosts with a multiple number of VMs on each hosting servers, and we incorporate (i) failure and recovery of hosting servers and VMs, (ii) VM high availability (HA) and (iii) VM live migration (LM). The VDCs with/without using VM HA and LM are compared in terms of capacity oriented availability (i.e., number of available VMs).
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modeling and analysis of software rejuvenation in a server Virtualized System with live vm migration
Performance Evaluation, 2013Co-Authors: Kishor S. Trivedi, Fumio Machida, Dong Seong KimAbstract:As server virtualization is used in a number of IT Systems, the unavailability of virtual machines (VM) on server Virtualized Systems becomes a significant concern. Software rejuvenation is a promising technique for improving the availability of server Virtualized Systems as it can postpone or prevent failures caused by software aging in both the VM and the underlying virtual machine monitor (VMM). In this paper, we study the effectiveness of a combination of VMM rejuvenation and live VM migration. When a VMM needs to be rejuvenated, the hosted VMs running on the VMM can be moved to another host using live VM migration and continue the execution even during the VMM rejuvenation. We call this technique Migrate-VM rejuvenation and construct an availability model in the stochastic reward net for evaluating it in comparison with the conventional approaches; Cold-VM rejuvenation and Warm-VM rejuvenation. The designed model enables us to find the optimum combinations of rejuvenation trigger intervals that maximize the availability of VM. In terms of the maximum VM availability, Migrate-VM rejuvenation is potentially the best approach. However, the advantage of Migrate-VM rejuvenation depends on the type of live VM migration (stop-and-copy or pre-copy) and the policy for migration back to the original host after VMM rejuvenation (return-back or stay-on). Through numerical examples, we show that ''pre-copy'' live VM migration is encouraged rather than pure ''stop-and-copy'' migration and it is better to return back VM to the original host soon after the VMM rejuvenation (i.e., ''return-back'' rather than ''stay-on'' policy) for high-availability. The effect of the VMM rejuvenation technique on the expected number of transactions lost is also studied by combining the availability model with an M/M/1/n queueing model.
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Sensitivity Analysis of Server Virtualized System Availability
IEEE Transactions on Reliability, 2012Co-Authors: Rubens Matos, Dong Seong Kim, Fumio Machida, Paulo Maciel, Kishor S. TrivediAbstract:Server virtualization is a technology used in many enterprise Systems to reduce operation and acquisition costs, and increase the availability of their critical services. Virtualized Systems may be even more complex than traditional nonVirtualized Systems; thus, the quantitative assessment of System availability is even more difficult. In this paper, we propose a sensitivity analysis approach to find the parameters that deserve more attention for improving the availability of Systems. Our analysis is based on Markov reward models, and suggests that host failure rate is the most important parameter when the measure of interest is the System mean time to failure. For capacity oriented availability, the failure rate of applications was found to be another major concern. The results of both analyses were cross-validated by varying each parameter in isolation, and checking the corresponding change in the measure of interest. A cost-based optimization method helps to highlight the parameter that should have higher priority in System enhancement.
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Modeling and analysis of software rejuvenation in a server Virtualized System
2010 IEEE Second International Workshop on Software Aging and Rejuvenation, 2010Co-Authors: Fumio Machida, Dong Seong Kim, Kishor S. TrivediAbstract:As server virtualization is used as an essential software infrastructure of various software services such as cloud computing, availability management of server Virtualized System is becoming more significant. Although time-based software rejuvenation is useful to postpone/prevent failures due to software aging in a server Virtualized System, the rejuvenation schedules for virtual machine (VM) and virtual machine monitor (VMM) need to be determined in a proper way for the VM availability, since VMM rejuvenation affects VMs running on the VMM. This paper presents analytic models using stochastic reward nets for three time-based rejuvenation techniques of VMM; (i) Cold-VM rejuvenation in which all VMs are shut down before the VMM rejuvenation, (ii) Warm-VM rejuvenation in which all VMs are suspended before the VMM rejuvenation and (iii) Migrate-VM rejuvenation in which all VMs are moved to the other host server during the VMM rejuvenation. We compare the three techniques in terms of steady-state availability and the number of transactions lost in a year. We find the optimal combination of rejuvenation trigger intervals for each rejuvenation technique by a gradient search method. The numerical analysis shows the interesting result that Warm-VM rejuvenation does not always outperform Cold-VM rejuvenation in terms of steady-state availability depending on rejuvenation trigger intervals. Migrate-VM rejuvenation is better than the other two as long as live VM migration rate is large enough and the other host server has a capacity to accept the migrated VM.
Fumio Machida - One of the best experts on this subject based on the ideXlab platform.
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Analyzing Software Rejuvenation Techniques in a Virtualized System: Service Provider and User Views
IEEE Access, 2020Co-Authors: Jing Bai, Kishor S. Trivedi, Fumio Machida, Xiaolin Chang, Zhen HanAbstract:Virtualization technology has promoted the fast development and deployment of cloud computing, and is now becoming an enabler of Internet of Everything. Virtual machine monitor (VMM), playing a critical role in a Virtualized System, is software and hence it suffers from software aging after a long continuous running as well as software crashes due to elusive faults. Software rejuvenation techniques can be adopted to reduce the impact of software aging. Although there existed analytical model-based approaches for evaluating software rejuvenation techniques, none analyzed both application service (AS) availability and job completion time in a Virtualized System with live virtual machine (VM) migration. This paper aims to quantitatively analyze software rejuvenation techniques from service provider and user views in a Virtualized System deploying VMM reboot and live VM migration techniques for rejuvenation, under the condition that all the aging time, failure time, VMM fixing time and live VM migration time follow general distributions. We construct an analytical model by using a semi-Markov process (SMP) and derive formulas for calculating AS availability and job completion time. By analytical experiments, we can obtain the optimal migration trigger intervals for achieving the approximate maximum AS availability and the approximate minimum job completion time, and then service providers can make decisions for maximizing the benefits of service providers and users by adjusting parameter values.
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CIT - Availability Modeling and Analysis of a Virtualized System Using Stochastic Reward Nets
2016 IEEE International Conference on Computer and Information Technology (CIT), 2016Co-Authors: Dong Seong Kim, Fumio Machida, Jin B. Hong, Tuan A.h. Nguyen, Jong Sou Park, Kishor S. TrivediAbstract:Availability is one of the key requirements for modern networked System. Availability of a Virtualized System can be modelled and analyzed using stochastic models. In our previous work, availability of a Virtualized System was modeled using a hierarchical model to incorporate the detailed behavior of virtual machines (VMs)' failure and recovery with respect to the System behavior. In particular, a truncated continuous time Markov chain model was used for VM mode. In this paper, we propose to construct a stochastic reward nets (SRN) to model and analyze the availability of a Virtualized System. Further, we study the effect on the availability when restrictions on the guard functions are relaxed. We use a Virtualized data center (VDC) using three hosts with a multiple number of VMs on each hosting servers, and we incorporate (i) failure and recovery of hosting servers and VMs, (ii) VM high availability (HA) and (iii) VM live migration (LM). The VDCs with/without using VM HA and LM are compared in terms of capacity oriented availability (i.e., number of available VMs).
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modeling and analysis of software rejuvenation in a server Virtualized System with live vm migration
Performance Evaluation, 2013Co-Authors: Kishor S. Trivedi, Fumio Machida, Dong Seong KimAbstract:As server virtualization is used in a number of IT Systems, the unavailability of virtual machines (VM) on server Virtualized Systems becomes a significant concern. Software rejuvenation is a promising technique for improving the availability of server Virtualized Systems as it can postpone or prevent failures caused by software aging in both the VM and the underlying virtual machine monitor (VMM). In this paper, we study the effectiveness of a combination of VMM rejuvenation and live VM migration. When a VMM needs to be rejuvenated, the hosted VMs running on the VMM can be moved to another host using live VM migration and continue the execution even during the VMM rejuvenation. We call this technique Migrate-VM rejuvenation and construct an availability model in the stochastic reward net for evaluating it in comparison with the conventional approaches; Cold-VM rejuvenation and Warm-VM rejuvenation. The designed model enables us to find the optimum combinations of rejuvenation trigger intervals that maximize the availability of VM. In terms of the maximum VM availability, Migrate-VM rejuvenation is potentially the best approach. However, the advantage of Migrate-VM rejuvenation depends on the type of live VM migration (stop-and-copy or pre-copy) and the policy for migration back to the original host after VMM rejuvenation (return-back or stay-on). Through numerical examples, we show that ''pre-copy'' live VM migration is encouraged rather than pure ''stop-and-copy'' migration and it is better to return back VM to the original host soon after the VMM rejuvenation (i.e., ''return-back'' rather than ''stay-on'' policy) for high-availability. The effect of the VMM rejuvenation technique on the expected number of transactions lost is also studied by combining the availability model with an M/M/1/n queueing model.
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Sensitivity Analysis of Server Virtualized System Availability
IEEE Transactions on Reliability, 2012Co-Authors: Rubens Matos, Dong Seong Kim, Fumio Machida, Paulo Maciel, Kishor S. TrivediAbstract:Server virtualization is a technology used in many enterprise Systems to reduce operation and acquisition costs, and increase the availability of their critical services. Virtualized Systems may be even more complex than traditional nonVirtualized Systems; thus, the quantitative assessment of System availability is even more difficult. In this paper, we propose a sensitivity analysis approach to find the parameters that deserve more attention for improving the availability of Systems. Our analysis is based on Markov reward models, and suggests that host failure rate is the most important parameter when the measure of interest is the System mean time to failure. For capacity oriented availability, the failure rate of applications was found to be another major concern. The results of both analyses were cross-validated by varying each parameter in isolation, and checking the corresponding change in the measure of interest. A cost-based optimization method helps to highlight the parameter that should have higher priority in System enhancement.
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Modeling and analysis of software rejuvenation in a server Virtualized System
2010 IEEE Second International Workshop on Software Aging and Rejuvenation, 2010Co-Authors: Fumio Machida, Dong Seong Kim, Kishor S. TrivediAbstract:As server virtualization is used as an essential software infrastructure of various software services such as cloud computing, availability management of server Virtualized System is becoming more significant. Although time-based software rejuvenation is useful to postpone/prevent failures due to software aging in a server Virtualized System, the rejuvenation schedules for virtual machine (VM) and virtual machine monitor (VMM) need to be determined in a proper way for the VM availability, since VMM rejuvenation affects VMs running on the VMM. This paper presents analytic models using stochastic reward nets for three time-based rejuvenation techniques of VMM; (i) Cold-VM rejuvenation in which all VMs are shut down before the VMM rejuvenation, (ii) Warm-VM rejuvenation in which all VMs are suspended before the VMM rejuvenation and (iii) Migrate-VM rejuvenation in which all VMs are moved to the other host server during the VMM rejuvenation. We compare the three techniques in terms of steady-state availability and the number of transactions lost in a year. We find the optimal combination of rejuvenation trigger intervals for each rejuvenation technique by a gradient search method. The numerical analysis shows the interesting result that Warm-VM rejuvenation does not always outperform Cold-VM rejuvenation in terms of steady-state availability depending on rejuvenation trigger intervals. Migrate-VM rejuvenation is better than the other two as long as live VM migration rate is large enough and the other host server has a capacity to accept the migrated VM.
Seongwook Jin - One of the best experts on this subject based on the ideXlab platform.
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architectural support for secure virtualization under a vulnerable hypervisor
International Symposium on Microarchitecture, 2011Co-Authors: Seongwook Jin, Jeongseob Ahn, Sanghoon Cha, Jaehyuk HuhAbstract:Although cloud computing has emerged as a promising future computing model, security concerns due to malicious tenants have been deterring its fast adoption. In cloud computing, multiple tenants may share physical Systems by using virtualization techniques. In such a Virtualized System, a software hypervisor creates virtual machines (VMs) from the physical System, and provides each user with an isolated VM. However, the hypervisor, with a full control over hardware resources, can access the memory pages of guest VMs without any restriction. By compromising the hypervisor, a malicious user can access the memory contents of the VMs used by other users. In this paper, we propose a hardware-based mechanism to protect the memory of guest VMs from unauthorized accesses, even with an untrusted hypervisor. With this mechanism, memory isolation is provided by the secure hardware, which is much less vulnerable than the software hypervisor. The proposed mechanism extends the current hardware support for memory virtualization with a small extra hardware cost. The hypervisor can still flexibly allocate physical memory pages to virtual machines for efficient resource management. However, the hypervisor can update nested page tables only through the secure hardware mechanism, which verifies each mapping change. Using the hardware-oriented mechanism in each System securing guest VMs under a vulnerable hypervisor, this paper also proposes a cloud System architecture, which supports the authenticated launch and migration of guest VMs.
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MICRO - Architectural support for secure virtualization under a vulnerable hypervisor
Proceedings of the 44th Annual IEEE ACM International Symposium on Microarchitecture - MICRO-44 '11, 2011Co-Authors: Seongwook Jin, Jeongseob Ahn, Sanghoon Cha, Jaehyuk HuhAbstract:Although cloud computing has emerged as a promising future computing model, security concerns due to malicious tenants have been deterring its fast adoption. In cloud computing, multiple tenants may share physical Systems by using virtualization techniques. In such a Virtualized System, a software hypervisor creates virtual machines (VMs) from the physical System, and provides each user with an isolated VM. However, the hypervisor, with a full control over hardware resources, can access the memory pages of guest VMs without any restriction. By compromising the hypervisor, a malicious user can access the memory contents of the VMs used by other users. In this paper, we propose a hardware-based mechanism to protect the memory of guest VMs from unauthorized accesses, even with an untrusted hypervisor. With this mechanism, memory isolation is provided by the secure hardware, which is much less vulnerable than the software hypervisor. The proposed mechanism extends the current hardware support for memory virtualization with a small extra hardware cost. The hypervisor can still flexibly allocate physical memory pages to virtual machines for efficient resource management. However, the hypervisor can update nested page tables only through the secure hardware mechanism, which verifies each mapping change. Using the hardware-oriented mechanism in each System securing guest VMs under a vulnerable hypervisor, this paper also proposes a cloud System architecture, which supports the authenticated launch and migration of guest VMs.
Dong Seong Kim - One of the best experts on this subject based on the ideXlab platform.
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CIT - Availability Modeling and Analysis of a Virtualized System Using Stochastic Reward Nets
2016 IEEE International Conference on Computer and Information Technology (CIT), 2016Co-Authors: Dong Seong Kim, Fumio Machida, Jin B. Hong, Tuan A.h. Nguyen, Jong Sou Park, Kishor S. TrivediAbstract:Availability is one of the key requirements for modern networked System. Availability of a Virtualized System can be modelled and analyzed using stochastic models. In our previous work, availability of a Virtualized System was modeled using a hierarchical model to incorporate the detailed behavior of virtual machines (VMs)' failure and recovery with respect to the System behavior. In particular, a truncated continuous time Markov chain model was used for VM mode. In this paper, we propose to construct a stochastic reward nets (SRN) to model and analyze the availability of a Virtualized System. Further, we study the effect on the availability when restrictions on the guard functions are relaxed. We use a Virtualized data center (VDC) using three hosts with a multiple number of VMs on each hosting servers, and we incorporate (i) failure and recovery of hosting servers and VMs, (ii) VM high availability (HA) and (iii) VM live migration (LM). The VDCs with/without using VM HA and LM are compared in terms of capacity oriented availability (i.e., number of available VMs).
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modeling and analysis of software rejuvenation in a server Virtualized System with live vm migration
Performance Evaluation, 2013Co-Authors: Kishor S. Trivedi, Fumio Machida, Dong Seong KimAbstract:As server virtualization is used in a number of IT Systems, the unavailability of virtual machines (VM) on server Virtualized Systems becomes a significant concern. Software rejuvenation is a promising technique for improving the availability of server Virtualized Systems as it can postpone or prevent failures caused by software aging in both the VM and the underlying virtual machine monitor (VMM). In this paper, we study the effectiveness of a combination of VMM rejuvenation and live VM migration. When a VMM needs to be rejuvenated, the hosted VMs running on the VMM can be moved to another host using live VM migration and continue the execution even during the VMM rejuvenation. We call this technique Migrate-VM rejuvenation and construct an availability model in the stochastic reward net for evaluating it in comparison with the conventional approaches; Cold-VM rejuvenation and Warm-VM rejuvenation. The designed model enables us to find the optimum combinations of rejuvenation trigger intervals that maximize the availability of VM. In terms of the maximum VM availability, Migrate-VM rejuvenation is potentially the best approach. However, the advantage of Migrate-VM rejuvenation depends on the type of live VM migration (stop-and-copy or pre-copy) and the policy for migration back to the original host after VMM rejuvenation (return-back or stay-on). Through numerical examples, we show that ''pre-copy'' live VM migration is encouraged rather than pure ''stop-and-copy'' migration and it is better to return back VM to the original host soon after the VMM rejuvenation (i.e., ''return-back'' rather than ''stay-on'' policy) for high-availability. The effect of the VMM rejuvenation technique on the expected number of transactions lost is also studied by combining the availability model with an M/M/1/n queueing model.
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Sensitivity Analysis of Server Virtualized System Availability
IEEE Transactions on Reliability, 2012Co-Authors: Rubens Matos, Dong Seong Kim, Fumio Machida, Paulo Maciel, Kishor S. TrivediAbstract:Server virtualization is a technology used in many enterprise Systems to reduce operation and acquisition costs, and increase the availability of their critical services. Virtualized Systems may be even more complex than traditional nonVirtualized Systems; thus, the quantitative assessment of System availability is even more difficult. In this paper, we propose a sensitivity analysis approach to find the parameters that deserve more attention for improving the availability of Systems. Our analysis is based on Markov reward models, and suggests that host failure rate is the most important parameter when the measure of interest is the System mean time to failure. For capacity oriented availability, the failure rate of applications was found to be another major concern. The results of both analyses were cross-validated by varying each parameter in isolation, and checking the corresponding change in the measure of interest. A cost-based optimization method helps to highlight the parameter that should have higher priority in System enhancement.
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Modeling and analysis of software rejuvenation in a server Virtualized System
2010 IEEE Second International Workshop on Software Aging and Rejuvenation, 2010Co-Authors: Fumio Machida, Dong Seong Kim, Kishor S. TrivediAbstract:As server virtualization is used as an essential software infrastructure of various software services such as cloud computing, availability management of server Virtualized System is becoming more significant. Although time-based software rejuvenation is useful to postpone/prevent failures due to software aging in a server Virtualized System, the rejuvenation schedules for virtual machine (VM) and virtual machine monitor (VMM) need to be determined in a proper way for the VM availability, since VMM rejuvenation affects VMs running on the VMM. This paper presents analytic models using stochastic reward nets for three time-based rejuvenation techniques of VMM; (i) Cold-VM rejuvenation in which all VMs are shut down before the VMM rejuvenation, (ii) Warm-VM rejuvenation in which all VMs are suspended before the VMM rejuvenation and (iii) Migrate-VM rejuvenation in which all VMs are moved to the other host server during the VMM rejuvenation. We compare the three techniques in terms of steady-state availability and the number of transactions lost in a year. We find the optimal combination of rejuvenation trigger intervals for each rejuvenation technique by a gradient search method. The numerical analysis shows the interesting result that Warm-VM rejuvenation does not always outperform Cold-VM rejuvenation in terms of steady-state availability depending on rejuvenation trigger intervals. Migrate-VM rejuvenation is better than the other two as long as live VM migration rate is large enough and the other host server has a capacity to accept the migrated VM.
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WoSAR@ISSRE - Modeling and analysis of software rejuvenation in a server Virtualized System
2010 IEEE Second International Workshop on Software Aging and Rejuvenation, 2010Co-Authors: Fumio Machida, Dong Seong Kim, Kishor S. TrivediAbstract:As server virtualization is used as an essential software infrastructure of various software services such as cloud computing, availability management of server Virtualized System is becoming more significant. Although time-based software rejuvenation is useful to postpone/prevent failures due to software aging in a server Virtualized System, the rejuvenation schedules for virtual machine (VM) and virtual machine monitor (VMM) need to be determined in a proper way for the VM availability, since VMM rejuvenation affects VMs running on the VMM. This paper presents analytic models using stochastic reward nets for three time-based rejuvenation techniques of VMM; (i) Cold-VM rejuvenation in which all VMs are shut down before the VMM rejuvenation, (ii) Warm-VM rejuvenation in which all VMs are suspended before the VMM rejuvenation and (iii) Migrate-VM rejuvenation in which all VMs are moved to the other host server during the VMM rejuvenation. We compare the three techniques in terms of steady-state availability and the number of transactions lost in a year. We find the optimal combination of rejuvenation trigger intervals for each rejuvenation technique by a gradient search method. The numerical analysis shows the interesting result that Warm-VM rejuvenation does not always outperform Cold-VM rejuvenation in terms of steady-state availability depending on rejuvenation trigger intervals. Migrate-VM rejuvenation is better than the other two as long as live VM migration rate is large enough and the other host server has a capacity to accept the migrated VM.
