Live Migration of Virtual Machines
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Live Migration of Virtual
MachinesChristopher Clark, Keir Fraser, Steven Hand, Jacob Gorm Hansen†,Eric Jul†, Christian Limpach, Ian Pratt, Andrew Warfield
University of Cambridge Computer Laboratory† Department of Computer Science ,University of Copenhagen, Denmark
USENIX NSDI ‘05
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IntroductionOperating system virtualization has
attracted considerable interest in recent years-In data Centers, cluster computing communities
allows many OS instances to run concurrently on a single physical machine
Migrating an entire OS and all of its applications as one unit◦ Compared to the process migration (residual
dependencies)
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IntroductionLive Migration
Without interfering the network connection
Allows a separation of concerns between the users and operator of a datacenter or cluster.
Allowing separation of hardware and software considerations
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IntroductionDowntime
◦services are entirely unavailableTotal migration time
during which state on both machines is synchronized and which hence may affect reliability
This paper use the “pre-copy” approach to achieve live migration and target on decreasing the downtime (implemented on Xen)
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DesignNetwork
Generate an ARP reply from the migrated host, advertising that the IP has moved to a new location.
StorageUse a network-attached storage (NAS) deviceDo not need to migrate disk storage
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DesignMemory Transfer
◦ Push phase◦ Stop-and-copy phase◦ Pull phase
most practical solutions select one or two of the three phases ◦ pure stop-and-copy, pure demand
This paper uses iterative push phase with a typically very short stop-and-copy phase.
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Related WorkShutdown the VMPre-CopyVMware
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Related WorkPost-Copy Live Migration of
Virtual Machines Michael R. Hines, Umesh Deshpande, and Kartik
GopalanComputer Science, Binghamton University (SUNY)
ACM SIGPLAN/SIGOPS VEE’09
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Design Overview
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WritableWorking SetsSome pages will seldom or never be
modified and hence are good candidates for pre-copy
Some will be written often and so should best be transferred via stop-and-copy
=> WritableWorking Sets
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WritableWorking Sets
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WritableWorking Sets
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Dynamic Rate-LimitingDynamically adapt the bandwidth limit
during each pre-copying round
The administrator selects a minimum(m) and a maximum(M) bandwidth limit
The first pre-copy round transfers pages at the minimum bandwidth m
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Dynamic Rate-LimitingDirtying rate =
(the number of pages dirtied in the previous round)/ (duration of the previous round)
Bandwidth rate for next round = Dirtying rate + 50 Mbits/sec
Stop pre-copy when◦ Calculated rate > M◦ Less than 256KB remains to be tranferred
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Some implementation issuesRapid Page Dirtying
◦Do not need to always transfer hot pages
Freeing Page Cache Pages◦In the first round
Stunning Rogue Processes◦ Limit each process to 40 write faults each time
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Stunning Rogue Processes
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EvaluationDell PE-2650 server-class
machinesdual Xeon 2GHz CPUs2GB memoryconnected via Gigabit EthernetStorage: iSCSI protocol NASXenLinux 2.4.27
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a. SimpleWeb ServerApache 1.3 web serverContinuously serving a single
512KB filememory allocation: 800MBInitially rate limited to
100Mbit/sec776MB memory to be transferred
in the first round165ms outage
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a. SimpleWeb Server
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b.ComplexWebWorkload:SPECweb99memory allocation: 800MB30% require dynamic content
generation16% are HTTP POST operations0.5% execute a CGI scriptThe server generates access and
POST logs210ms outage
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b.ComplexWebWorkload:SPECweb99
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c. Low-Latency Server: Quake 3a multiplayer on-line game
servera virtual machine with 64MB of
memorySix players joined the game and
started to play within a shared arena
transfers so little data (148KB) in the last round
Downtime: 60ms
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c. Low-Latency Server: Quake 3
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d. A DiabolicalWorkload: MMunchera virtual machine is writing to
memory faster than can be transferred
Memory: 512MBa simple C program that writes
constantly to a 256MBDowntime: 3.5 seconds
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d. A DiabolicalWorkload: MMuncher
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ConclusionA pre-copy live migration method
on XenConcern about WWSDynamic network-bandwidth
adaptionrealistic server workloads such as
SPECweb99 can be migrated with just 210ms downtime
a Quake3 game server is migrated with an imperceptible 60ms outage