HP Integrity Virtual Machines 4.2: Installation, Configuration, and Administration

Figure 10-2 Online Guest Migration from Source to Target
-
Guest OS
app1 app2
SAN
Guest continues to operate
on source host while
migration begins
Guest continues operation
on target server after
transfer completes
Guest is briefly
suspended as final
resident memory
image transfers
Guest OS with unique:
Kernel Parameters
Patch levels
Layered software
Guest OS
app1 app2
Source Host (Intergrity VM and HP-UX)
Target Host (Intergrity VM and HP-UX)
10.1.1 Reasons for Migrating an Online Guest
There are various reasons why you might want to migrate an online guest. Most can be
summarized into three categories:
• Vacating a VM Host system
• Targeting a particular VM Host
• Balancing VM Host workloads
• Optimizing physical resource utilization
With Online VM Migration, you can migrate all your guests off of a VM Host to one or more
other VM Hosts without interrupting the workload activity on the guests. A common reason to
do this is for maintenance of the VM Host system: hardware, firmware or software. You can
configure the hardware that does not have hot-plug support. You can update the firmware,
which requires the system to be shut down. You can also update software components that
require a VM Host reboot. A rolling upgrade of VM Host software is possible by moving the
running guests to another VM Host, upgrading the VM Host, then migrating the guests back.
Being able to move guests while keeping active applications online allows greater flexibility in
scheduling maintenance or upgrades, and minimizes the impact of unpredictable maintenance.
For example, you can move online guests in response to predictive failure alerts without
interrupting your applications.
You might also want to migrate an active guest workload to a particular VM Host to take
advantage of a particular resource or feature on that target VM Host without losing application
availability. If your current VM Host resources become oversubscribed, you can migrate one or
more of the guests to other VM Hosts that have remaining capacity. Perhaps a potential target
VM Host has a large quantity of RAM, CPUs or I/O adapters, which might facilitate faster
processing or greater I/O bandwidth while on that VM Host. Another possibility is that certain
VM Hosts have special devices that are needed only temporarily by guest workloads. Because
Online VM Migration enables guests to be migrated without interrupting their workloads, it is
convenient and practical to migrate guests temporarily to certain VM Hosts to take advantage
of their particular resources and features when they are needed. This is especially true for
workloads with well-understood cyclic resource requirements (for example, month-end
processing).
10.1 Introduction to Virtual Machine Migration 167