XEN Virtualization, the Host System and Overhead

Question

so some colleagues and me are planning to merge our VPS Servers to one big standalone and each participant gets a separate Virtual Machine.

We split the available resources, so each VM gets about one quarter of the host resources (minus the resources for the Host System).

This there any reference which (free) Virtualization to choose? I worked a lot with VMWare ESX Barebone Servers and the whole Infrastructure Packet of VMWare and liked it a lot.

What Host System should we take? I tending to choose Debian 5 Lenny over Ubuntu 9.04 for overall security and stability matters (the Host System is going to be the SPOF). Is 512 MB RAM enough? I googled a lot but didn't find any real guidelines what to do, so I'm asking your expert opinions :)

Any help is appreciated. Thanks!

Answer 1

Debian or Ubuntu are both suitable choices for your xen dom0.

As for resources, it's difficult to give strict recommendations because no two setups are the same and ultimately it depends on what your guests are going to be doing.

First up, you won't have all the memory in the physical system available for use in dom0 and your other guest. Xen will take a slice of the memory for itself. The more physical memory, the more xen will need.

The amount of dom0 memory you're going to need depends on the workload it's going to be handling with management of the guests and all the I/0 from the guests. It's difficult to quantify. 512MB may well be enough. In any case you can change if that isn't sufficient.

At a previous job we integrated xen server into our virtualisation platform. Dom0 was set to 768M, which did the job and I didn't come across any instances of this being exhausted by customers. This was on physical boxes with upto 64GB of memory. Another approach is to give all the available memory to dom0, and then slice chunks off each time you create a guest.

Answer 2

I'd use a debian dom0. If you're going with Xen the dom0 will need at least 100mb memory, but 256mb are preferred.

Since you like Vmwares Infrastructure, you should look into libvirt for management. kvm is a real alternative to xen, which has notoriously has problems with newer kernels.

I'd stay away from Vmware Server, since it performs badly. Vmware esx and XenSource might be an alternative unless you want to customize your linux installation, i.e. use dm-crypt or software raid.