There are some differences between KVM and OpenVZ. Down below is a summary with pron and cons for KVM and OpenVZ:
+ Full virtualization, so the behaviour as a dedicated/physical server
+ Linux, *BSD and Windows support (basically any OS that can be installed via ISO)
+ Dedicated resources (except the CPU / NIC which are shared)
+ Usage of OS templates, but also the ability to install the OS yourself.
+ Your own kernel and modules
+ Your own virtual disk, graphics adapter, network card
+ Generally more stable compared to OpenVZ
- More overhead on system resources (memory/disk), since each VPS has it's own kernel/OS.
KVM is great for anyone who like to have full control over their VPS, or is looking for the highest uptime.
As with all virtualization techniques, the CPU and network port are shared among all VPSes on this node.
For low memory VPSes (<256MB), you might want to consider OpenVZ as a KVM VPS has it's own kernel/OS which means extra memory usage.
+ Container style virtualization, shared kernel with the host
+ A very low memory footprint, since the OS shares the kernel with the OS. This makes OpenVZ a great choice for VPSes with a low amount of memory
+ A little bit better performance to KVM, since there is no additional virtualization layer between the host and your VPS, which means that there is basically no overhead on assigned CPU / memory and disk resources.
- OS templates only, there is no option to manual install your OS.
- Not all kernel modules available. Although most kernel modules are enabled at our side, there is still a chance that you require a special module which is, or can't be loaded from our side.
As with all virtualization techniques, the CPU and network port are shared with are shared among all VPSes on this node.
OpenVZ is usually a good choice for anyone that don't have special requirements.