The root partition of a virtual machine can be stored on a volume to prevent extended downtime from a hardware failure incident. Upon detection of a failed host node, VMs without local storage will be automatically booted on another host node.
To accomplish this, start by creating a new volume from the Volumes page. Select the region where you'll be provisioning the VM, a source template, and the desired disk size. If the disk size is equal to or smaller than that of the VM plan that you will use, then you won't be charged for the space; otherwise, each additional GB is $0.03/mo.
Note: if you already have a VM that you want to migrate to be on a volume, then you can take a snapshot of the VM, and then create the volume from the snapshot. Then, preserve the external IP address be de-associating the IP of the old VM and associate it with the new volume-backed VM.
Once the status of the volume is active/available, provision a VM from the volume (simply select the "My Volumes" tab when creating the VM). If you are using a template and are not using SSH keypair authentication, then you also need to check the "Set password via cloud-init" option.