HP Integrity Virtual Machines 4.2: Installation, Configuration, and Administration
You might want to segregate guests to balance the workload on VM Hosts workloads. For
example, you might want to separate guests whose workloads peak simultaneously. Or, perhaps
you want to group workloads together that have similar special resource requirements. For
example, you would usually run your multi-threaded applications on a VM Host that has several
CPUs in order to maximize the effectiveness of multi-way virtual machines. Online VM Migration
enables a new level of workload-to-resource alignment flexibility and agility -- you can segregate
or combine your workloads as you wish, without any interruption in application availability.
The Online VM Migration feature enables you to optimize the physical resources being used by
running guests. You can conveniently "park" idle, near-idle, or just currently less-critical guest
workloads together on a smaller or less powerful machine. You can use the dynamic memory
feature to reduce the amount of memory in use by the guests and shrink CPU entitlements to
more tightly pack guests on a smaller VM Host.
NOTE: Online migration of a guest from a V4.2 VM Host back to a V4.1 VM Host is not
supported with one exception. If a guest was originally booted on a V4.1 VM Host and then
migrated online to a V4.2 VM Host, you can perform an online migrate on that guest back to a
V4.1 VM Host.
10.1.2 Reasons for Migrating Virtual Machines Offline
This sections lists reasons why you might want to migrate a virtual machine offline. For example:
• The guest might be stopped, so you need to move the configuration information offline.
• Migrating the virtual machine offline does not use the VM Host resources (like memory and
CPUs) on the source and target VM Hosts.
• The guest might have local storage, logical volumes or file-backed storage, which must be
copied to the target VM Host.
• The source and target VM Hosts might have different processor types that prevent online
migration.
• The source VM Host might be running a version of Integrity VM prior to Version 4.2, which
does not support Online VM Migration.
• You can offline migrate guests between different processor families.
10.2 Command Line Interface for Online and Offline Migration
To migrate a virtual machine to another VM Host, perform the following steps:
1. Set up SSH keys on both the source and target hosts, as described in Section 10.3.2 (page 178).
2. Present all SAN storage assigned to the virtual machine to the target VM Host (if it is not
already there).
3. If using offline migration and the guest is booted, stop the guest on the source host, using
the hpvmstop or hpvmconsole command. You can also use the hpvmmigrate -d
command to stop the guest during the migration. This has an advantage in that resource
checks are made on the target before the guest is stopped on the source. However, for many
cases, it is actually best to log into the guest and shut it down before starting an offline
migration. This ensures that all guest data is properly flushed to the disks.
For information about starting and stopping guests, see Chapter 9 (page 141).
4. On the source host, enter the hpvmmigrate command, as described in Section 10.2.1
(page 169). When migrating an online guest, there are several reasons why the migration
might abort, leaving the guest running on the source host. Causes might include: insufficient
resources on the target host, excessively busy VM Hosts, a slow network connection, or an
extremely busy guest. If conditions like this exist, the attempted migration is aborted so the
guest's workload can continue running on the source host. This is not a serious problem,
because the migration can be re-attempted when conditions improve.
168 Migrating Virtual Machines