Hosts

Hosts, also known as hypervisors, are the physical servers on which virtual machines run. Full virtualization is provided by using a loadable Linux kernel module called Kernel-based Virtual Machine (KVM). KVM can concurrently host many virtual machines. Virtual machines run as individual Linux processes and threads on the host machine and are managed remotely by the engine.

Moving a Host to Maintenance Mode

Place a host into maintenance mode when performing common maintenance tasks, including network configuration and deployment of software updates, or before any event that might cause VDSM to stop working properly, such as a reboot, or issues with networking or storage.

When you place a host into maintenance mode the engine tries to migrate all running virtual machines to other hosts. The standard prerequisites for live migration apply, in particular there must be at least one active host in the cluster with capacity to run the migrated virtual machines.

Note:

Virtual machines that are pinned to the host can't be migrated and must be shut down before moving the host to maintenance mode. You can check which virtual machines are pinned to the host by selecting Pinned to Host in the Virtual Machines tab of the host’s details view.

Select Compute and then select Hosts.
Select the required host.
Select Management and then select Maintenance.
Optionally, enter a Reason for moving the host into maintenance mode, which appears in the logs and when the host is activated again. Then, select OK.

The host maintenance Reason field only appears if it has been enabled in the cluster settings.
Optionally, select the required options for hosts that support Gluster.

Select the Ignore Gluster Quorum and Self-Heal Validations option to avoid the default checks. By default, the Engine checks that the Gluster quorum isn't lost when the host is moved to maintenance mode. The Engine also checks that there's no self-heal activity that will be affected by moving the host to maintenance mode. If the Gluster quorum will be lost or if self-heal activity will be affected, the Engine prevents the host from being placed into maintenance mode. Only use this option if there is no other way to place the host in maintenance mode.

Select the Stop Gluster Service option to stop all Gluster services while moving the host to maintenance mode.

These fields only appear in the host maintenance window when the selected host supports Gluster.
Select OK to start maintenance mode.
All running virtual machines are migrated to other hosts. If the host is the Storage Pool Manager (SPM), the SPM role is migrated to another host. The Status field of the host changes to Preparing for Maintenance, and finally Maintenance when the operation completes successfully. VDSM doesn't stop while the host is in maintenance mode.

Note:

If migration fails on any virtual machine, select Management and then select Activate on the host to stop the operation placing it into maintenance mode, then select Cancel Migration on the virtual machine to stop the migration.

Activating a Host from Maintenance Mode

You must activate a host from maintenance mode before using it.

Select Compute and then select Hosts.
Select the host.
Select Management and then select Activate.
When complete, the host status changes to Unassigned, and finally Up.

Virtual machines can now run on the host. Virtual machines that were migrated off the host when it was placed into maintenance mode aren't automatically migrated back to the host when it's activated, but can be migrated manually. If the host was the Storage Pool Manager (SPM) before being placed into maintenance mode, the SPM role doesn't return automatically when the host is activated.

Removing a Host

You might need to remove a host from the Oracle Linux Virtualization Manager environment when upgrading to a newer version.

Select Compute and then select Hosts and select the host.
Select the host.
Select Management and then select Maintenance.
When the host is in maintenance mode, select Remove.

Select the Force Remove checkbox if the host is part of a Gluster Storage cluster and has volume bricks on it, or if the host is nonresponsive.
Select OK.