UCS 2.4 - Univention

6 Univention Virtual Machine Manager (UVMM)
Hard drive images can be administrated in two ways on KVM systems; by default images are saved in
the Extended format (qcow2). This format supports Copy-on-write which means that changes do not
overwrite the original version, but store new versions in different locations. The internal references of
the file administration are then updated to allow both access to the original and the new version. This
technique is a prerequisite for efficiently managing snapshots of virtual machines.
Alternatively, you can also access a hard drive image in Simple format (raw). Snapshots can only be
created when using hard drive images in Extended format.
Only the Simple format is available on Xen systems.
These image files are stored in so-called storage pools. Each virtualisation server already provides a
storage pool with the name Local directory in the default setting. This can be found on the virtualisation
servers in the /var/lib/libvirt/images directory.
If a live migration of virtual machines between different virtualisation servers is planned, the storage pool
must be stored on a system which can be accessed by all virtualisation servers (e.g., an NFS share or an
iSCSI target). This is described in [14].
Image files are created as sparse files with the specified size, i.e., these files only grow when they are
used and then up to the maximally specified size and thus initially require only minimal disk space.
It is also possible to provide a virtual machine with a disk drive via an image (in VFD format) or the
passthrough of a physical drive.
If drives are defined for a new virtual machine, it must be ensured that it is possible to boot from the
CDROM drive. The UVMM profile specifies the boot order for the fully-virtualised instances in advance.
For the paravirtualised instances, it is defined by the order on the definition of the drives and can be
adapted subsequently in the settings section.
Modifying a drive In the settings of a drive, Paravirtual drive allows specification of whether the access
to the drive should be paravirtualised. Where possible, this setting should not be changed for a virtual
machine which already has an operating system installed, as this may disrupt the access of partitions.
If drives or network interfaces are subsequently added to a virtual instance, the utilisation of paravirtuali-
sation is determined by heuristics.
If installation of a KVM-based Windows system with the virtIO drivers is planned, the setting must be
activated before beginning the Windows installation. Further information can be found under [14].
6.3.2.4 Network Interfaces
When a virtual machine is created, it is automatically assigned a network card with a randomly generated
MAC address.
This menu contains a list of all network cards; in addition, new cards can be added or existing ones edited.
The Type specifies the network connection. In the basic settings, a Bridge on the virtualisation server is
used to access the network directly. The virtual instance uses its own IP address for this.
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