Introduction to Virtualization - Oracle Solaris 10 System Virtualization Essentials - page 21

steps. The new system may need to be certified for proper installation and opera-
tion—another significant investment.
Virtualization provides useful separation between the VE and the hardware.
This containment simplifies the process of extracting a VE from the original sys-
tem and moving it to a new system. This operation, which is often called migra-
tion , is depicted in Figure 1.10.
Figure 1.10 Migrating a VE
Three types of migration are possible, each of which is characterized by the
amount of time during which the workload is not providing service, and by the
amount of workload state that is lost during the migration.
“Cold” migration is simply the orderly halting of the original environment and
its workload, the transfer of files from the old system to new storage or recon-
figuration of shared storage, followed by start-up on the new computer. If shared
storage is used to house the environment, this process is straightforward and does
not require a lengthy service outage. If the application should retain its state,
however, it might be necessary to save that state to persistent storage and reload
the information when the VE restarts.
“Warm” migration and “live” migration do not require halting and rebooting
the VE. Unlike cold migration, processes are not shut down during use of these
methods, so they maintain the state of their current activities. Warm migration,
shown in Figure 1.11, implies a noticeable service outage, usually on the order of
tens of seconds. During that period, the system effectively pauses the VE in its
original system, creates a new VE in the destination system, and copies a memory
image of the related processes to the target system. The processes then continue
their execution on the target system and the memory image for those processes on
the original system is destroyed.