OSDI '02 Abstract
Optimizing the Migration of Virtual Computers
Constantine P. Sapuntzakis, Ramesh Chandra, Ben Pfaff, Jim Chow, Monica S. Lam, and Mendel Rosenblum, Stanford University
This paper shows how to quickly move the state of a running
computer across a network, including the state in its
disks, memory, CPU registers, and I/O devices. We call
this state a capsule. Capsule state is hardware state, so it
includes the entire operating system as well as applications
and running processes.
We have chosen to move x86 computer states because
x86 computers are common, cheap, run the software we
use, and have tools for migration. Unfortunately, x86
capsules can be large, containing hundreds of megabytes
of memory and gigabytes of disk data. We have developed
techniques to reduce the amount of data sent over
the network: copy-on-write disks track just the updates
to capsule disks, "ballooning" zeros unused memory, demand
paging fetches only needed blocks, and hashing
avoids sending blocks that already exist at the remote
end. We demonstrate these optimizations in a prototype
system that uses VMware GSX Server virtual machine
monitor to create and run x86 capsules. The system targets
networks as slow as 384 kbps.
Our experimental results suggest that efficient capsule
migration can improve user mobility and system management.
Software updates or installations on a set of
machines can be accomplished simply by distributing a
capsule with the new changes. Assuming the presence of
a prior capsule, the amount of traffic incurred is commensurate
with the size of the update or installation package
itself. Capsule migration makes it possible for machines
to start running an application within 20 minutes on a
384 kbps link, without having to first install the application
or even the underlying operating system. Furthermore,
users' capsules can be migrated during a commute
between home and work in even less time.
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