Mark's blog

Introduction

I've been using and evaluating Citrix XenServer now for a while, and felt I should really post a review. I haven't seen much detailed coverage of this product at the level I'm interested in, so what follows is my take on it from a Unix Sysadmin's perspective. There won't be any funky screenshots or graphics; instead, I tried to cover the sort of things I wanted to know about when I was looking at it as a candidate for our virtualization solution at work.  

After all, implementing a new hypervisor is a big step, and a decision that you'll likely be stuck with for a long time. If there's anything else you'd like to know, just post in the comments section and I'll do my best to answer.

As some background: I've been using the open source Xen hypervisor as a virtualization platform, alongside VMware for Windows hosts for a good few years now at work. Part of the reason for picking Xen was that it was the standard on the systems I inherited, and also it was free and well-supported on most Linux distributions at the time. To date, I have been using CentOS as a Dom0 - as it's a free "clone" of Red Hat Enterprise Linux, it follows the same support schedules (up to 2014 for RHEL/CentOS 5.x) and is supported by pretty much every hardware vendor out there. It also has the libvirt tools built into it, as well as up to date packages for storage infrastructure such as DRBD and open-iscsi. It's well supported, and even though it is a conservative "stable" distro, point releases occur regularly with back-ported drivers and user-land updates.

With some work, you can roll your own management tools and scripts, and end up with a very flexible solution. However, it lacks some management ease of use, particularly for other systems administrators who may not be totally comfortable in a Linux environment. We also wanted to standardise on one virtualization platform if possible, and this all coincided nicely with a planned upgrade/migration off the VMware stack.

XenServer therefore presents a very attractive proposition: A well known, widely tested and supported open source hypervisor, with a superior management stack. The basic product is free, although support and enterprise features are available for a price. The prices for the advanced features are very reasonable, all the more so when you compare against VMware's offerings. Also consider that the free product allows you to connect to a wide range of networked storage systems and includes live migration, something that the free ESXi doesn't offer.

All of what follows covers the freely downloadable XenServer 5.6; Both Dell and HP offer embedded versions for some of their servers, however running and managing these systems should be near enough identical apart from the installation steps.

Update : Just after writing this, the beta of "FP1" (an update to XenServer 5.6) was announced. Full details of what will be in this update are here in the release notes. It looks like there will be plenty of significant improvements across all areas (including MPP RDAC, scheduled backups, supported jumbo frames, on-line coalescing of snapshot space and various other things of particular interest to me). Bear in mind when reading this review, that many of the little issues I have with XenServer may well be resolved in the upcoming version, and other areas may be totally overhauled. As soon as the final version is released I'll post a full update...

Update 2 : FP1 is indeed a big improvement. I've been using it in production now for a few months and should have an update soon, covering the new features such as the distributed switch, self-service portal etc.

Click the "Continue reading" link for the full review.