It is possible to start as many virtual machines as your hardware supports. Basically it is limited by system memory. Before you start a virtual machine instance you need to select the host name to use. The command network lookup presents a list of names the DNS can resolve. Next you need to choose the virtual machine template to be used as the source. Get a list of all locally available templates with template list.
There are two different modes of creating a virtual machine instance, cloning and shadowing. Using the command clone will create an independent copy of your virtual machine template, using potentially a lot of disk space. In contrast shadow will only create a virtual machine disk image to store differentials to the template disk image, thus saving local storage space.
Both commands have identical command line syntax:
vm clone|shadow TEMPLATE HOSTNAME
Virtual machine shadows to a virtual machine template can not be used standalone. You can check whether an instance is a shadow or a clone with the command image info, e.g.:
$ vm cd lxdev01
$ vm image info
image: /srv/vms/instances/lxdev01.devops.test/disk.img
file format: qcow2
virtual size: 40G (42949672960 bytes)
disk size: 6.3M
cluster_size: 65536
backing file: /srv/vms/images/debian64-6.0.4-basic/disk.img (actual path: /srv/vms/images/debian64-6.0.4-basic/disk.img)
In case you want to keep an independent virtual machine instance for an easy backup, it is recommended to only use clones.
Virtual machine instances cloned from a virtual machine template are completely decoupled (in contrast to a shadow). You can backup them simply by archiving their directory (make sure to shutdown the instance beforehand), e.g:
$ vm cd lxdev01
$ vm stop
$ tar -czf lxdev01.devops.test.kvm.tgz *
Now you can copy this archive to a save location or to another computer to use it there.