XEN PV v/s XEN HVM - Virtual Machine types in Citrix XEN

Xen PV:

Xen PV (short for Paravirtualization) is the most common form of Virtualization you will find with providers using Xen. Paravirtualization provides near-native performance and the appearence of isolation at the hardware level, in constrast to another equally popular virtualization platform called OpenVZ, which isolates at the OS or process level. This isolation provides a number of advantages, which is why Xen is often such a popular platform. It supports Linux only and operating systems are available in the form of pre-created templates, which can be deployed and rebuilt to in a matter of minutes.

A Xen PV VPS runs a complete and unmodified operating system and behaves exactly like a physical machine, exluding the kernel, bootloader and partition layout. By default a Xen PV VPS uses the same kernel that the host machine is running, but through a technology called Pygrub it is also possible to run your own kernel inside your VPS, e.g. the native kernel your favourite linux distribution provides. Despite not having full control over the kernel by default, you can compile and load your own kernel modules as you would on a real server.

Advantages:

•Complete and secure isolation

•Runs a full unmodified OS, excluding bootloader + kernel

•Can compile and load your own kernel modules

•Highly scalable, low overheads

•Easy OS reloads with precreated templates

•Direct allocations of RAM + HDD, not oversold and cannot be used by other VPS

•Easily upgraded/downgraded or migrated to another host machine if required

Disadvantages:

•Supports Linux only

•Limited to only the precreated OS templates

•Can't modify the OS options during install

•Can't compile and install a custom kernel unless using Pygrub

•Fixed two filesystem layout with two partitions, one for hdd one for swap

Xen HVM:

Xen HVM (short for Hardware-assited virtual machine) is becoming more and more popular, and offers the most flexability. Like PV, Xen HVM provides near-native performance although the overheads are slightly higher, and provides full hardware isolation, assisted by the Virtualization extensions in modern Processors. In a nutshell this means it really is a Virtual Dedicated Server, allowing you to install any operating system, with complete control over every aspect of it including the kernel, bootloader, filesystems + partition layout.

With a VDS you get access to VNC (Like KVM over IP on a dedicated server), which can be accessed through SolusVM or with your favourite VNC client. You can then choose from our massive collection of ISO images, pick the OS you want, mount it on your VPS and install it exactly how you want it via VNC. We offer a number of automated installers if you don't need anything fancy, and if there is an OS you would like which isn't in the list, we will gladly add it for you.

Advantages:

•Complete and secure isolation

•Run Linux, Unix, BSD or Windows

•Customize your kernel, and even your partition layouts

•Behaves exactly like a real physical server

•Large ISO library updated reguarly

Disadvantages:

•Slower / more time comsuming re-installs

•Higher overheads than Xen PV

•More dificult to upgrade/downgrade or migrate to another host machine if required