Rob's Blog

Virtualisation on the cheap

In my last post I wrote about building an iSCSI-based SAN using cheap hardware and software. Now for the application layer – virtualisation! But how do we do this using cheap – or free – software?

Now, you’re probably thinking, “What’s the big deal? Microsoft, VMware and Xen provide free virtualisation products”, and you’d be right. However I’m trying to build in some kind of redundancy – being able to boot virtual machines on alternative machines in the event of a hardware failure. Now I’ve not worked with Microsoft’s Virtual Server enough to know if this is possible (my guess is no, due to file system restrictions), so my solution is based around VMware’s Virtual Server product.

The aim here is to get as high performance as possible, to dedicate as much of the server’s resources to virtual machines as possible and to achieve the ability to boot virtual machines on a pool of hardware. The traditional solution for this is VMware’s ESX server – part of the Virtual Infrastructure suite – to use their VMFS (Virtual Machine File System). However, this does work out expensive.

So how do we get around this? Well, we can start by building a minimal Linux host for VMware server. I wrote a short article (here) about this quite a while ago now, but it should still be relevant – with a few changes. Following on from my last article, we’ll need the iSCSI initiator package to enable connectivity to our SAN. We’ll also need some kind of clustered file system. Now, I have no personal experience of this outside of VMware’s VMFS, but in theory, something such as Lustre should do the same thing.

Now if you build a couple of hosts, connecting to the same iSCSI LUN, utilising a clustered file system, you should be able to swap Virtual Machines between hosts at will. I’m not sure what sort of locking Lustre provides but you should be careful not to attempt to boot the same VMDK on multiple systems – I’ve no idea what could happen if you try this, so only do so at your own risk!

If you’ve followed the steps in my previous article and this one, you should now have not only a working iSCSI SAN built on the cheap, but also a cheap method of introducing some HA into your Virtual Machines. All without having to buy VMware’s VI3 too! I don’t recommend doing any of these unless you’re a Linux expert – something I’m not – as you’ve got no friendly support people to call when it all goes wrong. But if you’re looking to save the pennies or just learn more about SANs in general and iSCSI and VMware in particular, this is one way of doing it.

This entry was posted on Sunday, February 25th, 2007 at 2:02 pm and is filed under Virtualisation. Find similar posts by selecting any of the following tags: iscsi, Virtualisation. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.