How to Migrate KVM VM to Another Host Step by Step

Why migrate a KVM VM?

Migrating a KVM VM to another host is a common practice when dealing with system maintenance, resource optimization, or hardware upgrades.

• Reduce downtime: During server maintenance or upgrades, by migrating virtual machines, their operating environment can be quickly switched to other hosts, reducing business interruption time caused by server maintenance.
• Make full use of hardware resources: The load conditions of different hosts may vary, and migrating virtual machines helps to balance the workload across all hosts, thereby fully utilizing the hardware performance of all hosts and improving resource utilization.

How to migrate VMs from KVM to another host step-by-step

When moving KVM to another host, first ensure that the hardware environments of the source and target hosts are compatible, preferably within the same local area network. At the same time, back up important data in the virtual machine to avoid data loss during the migration process.

This section will introduce how to perform a KVM cold migration with commands.

1. On the source host, use the command virsh shutdown [virtual machine name] to ensure the virtual machine is completely stopped.

For example, if the virtual machine name is "testvm," execute:

virsh shutdown testvm

2. Export the virtual machine configuration file as an XML file by running the command:

virshdumpxmlguest_name>/root/guest_name.xml

3. Use the scp command to copy the configuration files and virtual machine disk files to the target host.

For example, to copy the configuration file:

scp/root/guest_name.xmldestination_host_ip://etc/libvirt/qemu

To copy the disk file:

scp /var/lib/libvirt/images/testvm.qcow2 [target host IP]:/var/lib/libvirt/images/`. [Target host IP]:/var/lib/libvirt/images/

4. Log in to the target host and execute the command:

virsh define [configuration file.xml]

For example:

virsh define /etc/libvirt/qemu/testvm.xml

5. Use the command virsh start [virtual machine name] to start the virtual machine and check if it is running normally.

In the complex process of KVM virtual machine migration, data backup is a crucial step and serves as the cornerstone for ensuring business continuity and data security.

If any unexpected issues arise during the migration process, such as network interruptions or hardware failures, the backed-up data can become the last line of defense to save the business, helping users quickly restore the virtual machine to its normal state and significantly reducing the risk of data loss.

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FAQ for moving KVM to another host

Q: Can I migrate a VM between different KVM versions?

A: Migration is usually smooth between compatible KVM versions. However, it’s important to ensure both hosts use compatible versions of libvirt and KVM.

Q: Why did my KVM VM migration fail?

A: It could be a network issue or a configuration error. First, check the network connection to ensure that the two hosts can communicate properly. Then, carefully review the migration commands and configuration files to see if there are any spelling mistakes or incorrect parameter settings.

Q: The virtual machine cannot boot after migration. How can this be resolved?

A: After migration, the virtual machine cannot boot, possibly due to incorrect paths in the configuration file. Check if the path of the virtual machine disk files matches the actual path on the target host. If there are errors, manually modify the paths in the configuration file.

Conclusion

By following the steps outlined in this article, whether using live migration or offline migration, you can effectively migrate KVM virtual machines to another host.

Correct migration allows us to better manage and utilize server resources, ensuring the stable operation of the business. Whether using the command line for traditional migration or leveraging real-time migration technology for zero-downtime migration, we need to make thorough preparations before the operation and strictly follow the steps.