VSI OpenVMS on KVM

To view the properties of a disk file, use the following command, specifying the name of your disk file:

qemu-img info disk_file_name.qcow2

The output will look similar to the following:

image: disk.qcow2
file format: qcow2
virtual size: 1 GiB (1073741824 bytes)
disk size: 1 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    refcount bits: 16
    corrupt: false
    extended l2: false
Child node '/file':
    filename: disk.qcow2
    protocol type: file
    file length: 1 GiB (1074135040 bytes)
    disk size: 1 GiB
    Format specific information:
        extent size hint: 1048576

Note the difference between virtual size and disk size. The virtual size is the size that the file is allowed to expand to, whereas disk size specifies the actual space it takes up on the host machine.

If your disk is not fully allocated/thick-provisioned, the virtual size value is likely higher than the disk size value.

Before you create a disk, check the installation guide for your version of OpenVMS for the recommended disk size:

Below is an example of a command that creates a thick-provisioned 20 GB disk.

qemu-img create -f qcow2 -o preallocation=full disk_name.qcow2 20G

The arguments used in this command, along with the recommended options, are explained in the table below.

For the full documentation on the qemu-img command, refer to https://linux.die.net/man/1/qemu-img.

To resize a hard drive, use the qemu-img resize command. In the following example, the disk size is expanded by 10 GB.

qemu-img resize --preallocation=full -f qcow2 disk_name.qcow2 +10G

Notice the difference in syntax compared to creating a disk. Instead of using the -o switch, --preallocation=full is specified. This is necessary to keep the disk thick-provisioned, as by default, the resize command only extends the virtual size of the disk, it does not pre-allocate the space for it, effectively converting the disk to thin-provisioned, which is not supported on OpenVMS.

To attach a disk to an existing VM, you must first identify what device is next available for mounting.

The arguments used in this command, along with the recommended options, are explained in the table below.

For the full documentation on the virsh attach-disk command, refer to https://www.libvirt.org/manpages/virsh.html#attach-disk.

To convert a disk from one format to another, use the following command:

qemu-img convert -f raw -O qcow2 source.img destination.qcow2

Note that this command does not delete the original disk.

For the full documentation on the qemu-img convert command, refer to https://docs.openstack.org/image-guide/convert-images.html.

You can add an additional network interface to an existing virtual machine via CLI, GUI, or by editing XML directly.

Some installations will require network bridges to be configured. For example, if you have multiple virtual machines that need to communicate using the same physical network card.

A virtual bridge configuration will be dependent on the environment that it needs to work in. VSI recommends following the steps described in the Configuring and managing networking guide by Red Hat Enterprise Linux on how to configure a network bridge on your Linux machine.

Once the bridge has been created, you can replace the --network line in the virt-install command with the bridge interface, specifying the MAC of your bridge interface:

--network=bridge:bridge0,mac=bridge_interface_mac,model='virtio-net'

If you are using virtio-net, it is important that you understand the different types of virtio-net devices.

When you create a virtio-net device, the model type "virtio" will be used by default:

<interface type="network">
  <mac address="52:54:00:00:00:00"/>
  <source network="default"/>
  <model type="virtio"/>
  <address type="pci" domain="0x0000" bus="0x06" slot="0x00" function="0x0"/>
</interface>

However, the real model is either virtio-transitional or virtio-non-transitional. OpenVMS supports both models and will choose one for you by default.

In certain cases, it may be beneficial to explicitly set the model type to "virtio-non-transitional". You can do so by specifying the model type on the virt-install command or by editing the XML file.

For more information on the virtio device models, refer to https://libvirt.org/formatdomain.html#virtio-device-models.