Running Xen 98
David Martinjak writes "Running Xen: A Hands-On Guide to the Art of Virtualization was published by Prentice Hall, and authored by Jeanna N. Matthews, Eli M. Dow, Todd Deshane, Wenjin Hu, Jeremy Bongio, Patrick F. Wilbur, and Brendan Johnson. The book, which will be referred to as simply Running Xen, was a great resource on Xen and virtualization from the administration side. A wide range of topics was covered from installing Xen all the way up to managing virtual resources, including migrating guest environments. Overall, the explanations were concise and understandable; while the information was presented in a straightforward manner. Running Xen was definitely a useful resource for administering systems with Xen." Keep reading for the rest of David's review.
The flow of the book was intuitive, and reasonable; this was especially valuable for discussing a newer technology where the terms could be confusing. Fortunately, the authors kept the language clear so that the reader easily could understand the subject of discussion. This unambiguous presentation of content was a welcomed feature.
| Running Xen: A Hands-On Guide to the Art of Virtualization | |
| author | Jeanna N. Matthews, Eli M. Dow, Todd Deshane, Wenjin Hu, Jeremy Bongio, Patrick F. Wilbur, and Brendan Johnson |
| pages | 586 |
| publisher | Prentice Hall |
| rating | 9 |
| reviewer | David Martinjak |
| ISBN | 0132349663 |
| summary | A hands-on guide to virtualization with Xen |
Running Xen started with a thorough-enough explanation of virtualization. Several different approaches to virtualization were compared and contrasted, which should help the reader to understand where Xen resides in the whole domain. This first chapter was a great introduction as it provided just the right amount of information. At no point did I consider the explanations to be short or lacking; nor did I feel overloaded with details. The authors seemed adequately aware that the title of the book was Running Xen, and they stuck to that scope.
After the introduction, the book moved right into actually running Xen. This helped to keep the my attention on the subject, and tied back in to the proper flow of the material. At first, the chapter began with baby steps. It introduced the Xen LiveCD, and information on working within the Xen environment. Subsequent chapters moved into a more intermediate level of usage: installing Xen in a third-party distrobution, and running pre-built guest images. Popular third-party distrobutions such as Ubuntu, Gentoo, CentOS, and OpenSUSE were covered; and this section also included instructions for using compiled Xen binaries and building your own from source.
One of the topics I was most interested in was building a custom, minimal guest environment from a particular distro. Chapter 7, "Populating Guest Images", provided all of the information I was looking for along with some other interesting facts. The popular distros were covered again (Ubuntu, Gentoo, etc.), but this time a twist was added to the mix. "Populating Guest Images" started off with installing Windows XP in Xen. This was a complete surprise to me. If you prefer GNU/Linux on the server, but Windows XP on the desktop, and have been looking to consolidate with virtualization; this chapter is a must-read. The chapter also helped solidify the understanding of concepts presented earlier in the book. For example, the first chapter discussed two different types of guests: paravirtual (PV) and Hardware Virtual Machine (HVM). In "Populating Guest Images", the authors led the reader through building guests of each type. The process was presented in a logical fashion which was easy to follow, making the book that much more enjoyable.
Running Xen then moved on to putting the guests on the network. Chapter 10, "Network Configuration", covered several options for networking guest environments in Xen. It would be an understatement to say that this chapter was thorough. Overall, the authors did a great job explaining the differences between the networking options, and how to implement each one. Unfortunately the needs of the reader are variable, so this chapter overflowed with information. The upside was that readers with complex virtualized network segments will not be disappointed. The downside was that I, personally, only really needed a small percentage of the chapter's content. Therefore, much of the chapter was technically irrelevant to me individually.
There was one other unfortunate issue, which occurred in the next chapter. Chapter 11, "Securing a Xen System", contained syntax errors for iptables rules. Mainly one dash was used instead of two when specifying the destination port in some rules. For example, LISTING 11.10 displayed the syntax -dport which caused an error. However, the syntax was correct at other places in the book (LISTING 10.24, for example). Additionally, there was a problem on output formatting where the command prompt and output lines ran together in the print (LISTING 11.11). This could cause confusion for some readers intently following the text.
My only complaint with the book was that the chapter on network configuration seemed to be rather long. For a person working with Xen at a business level, especially mid-size to enterprise, this chapter provided an excellent amount of insight and information. But for the person at home building his/her own test server for simple purposes, much of the content in this chapter was overkill. Additionally the few syntax errors were eye-sores, but any person with iptables experience could easily identify and fix the problems. It is just in my opinion, a published book should be syntactically correct so that the reader is not presented with contradicting results; nor should the reader have to conduct additional searches to rectify mistakes from the book's pages. However, these items are minor and pale in comparison to the outstanding wealth of knowledge in the text.
This book is highly recommended for anyone interested in virtualization with Xen. In addition to the regular paperback, Running Xen is also available on Safari. The paperback additionally includes a coupon code for a 45-day pass to access the book via Safari online.
David Martinjak is a programmer, GNU/Linux addict, and the director of 2600 in Cincinnati, Ohio. He can be reached at david.martinjak@gmail.com.
You can purchase Running Xen: A Hands-On Guide to the Art of Virtualization from amazon.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
Nope. No one has heard of that book. (Score:4, Informative)
"What's the sound of one hand adjusting a timing belt?"
Comment removed (Score:5, Informative)
Re:Does XEN have a future? (Score:3, Informative)
KVM is nice and shows promise, but performance wise the paravirtualized approach of xen is still significantly faster (as in very-near-bare-metal, even significantly faster than vmware ESX on most loads).
VirtIO [lwn.net], which is in latest versions of KVM, paravirtualizes all the hardware and gives you almost all the benefit.
KVM is where things are going because as a poster said above, it avoids having to write all the drivers twice over [livejournal.com]. Xen dropped the ball by not working closely with the Linux kernel developers. Now XenSource have been bought out by a Microsoft proxy [theregister.co.uk], so the future for Linux & Xen is looking even less rosy.
As you say, Red Hat offers libvirt [libvirt.org] which hides the differences between virtualization systems, so for most administrators and application programmers, which system "wins" is not going to matter. (My personal opinion is that none of them will win outright, at least not for many many years - different approaches to virtualization are suitable for different areas).
Rich.
Re:Does XEN have a future? (Score:3, Informative)
Xen isn't a silver bullet (Score:2, Informative)
The two biggest issues that bit me:
1. I wanted to use external USB drives in a xen virtual machine. I can do PCI passthrough (exposing a whole PCI device) to a guest but only on linux. Solaris support doesn't exist yet and I think the FreeBSD support is still in the pipeline. Tough luck if you want to run, say, a kernel-based ZFS distro on a guest OS like I did. I ended up using a linux guest with para-virtualized PCI and zfs-fuse but I still have some memory leak issues that mean I have to restart the fuse daemon every so often - not ideal.
2. I wanted to virtualize an old windows PC used to run through web logfiles once a month. Xen can't virtualize DMA access so for hardware virtual machines like Windows XP, you end up with IO based disk access which uses MUCH more CPU than DMA access - especially for this sort of task.
Better than RedHat documentation (Score:3, Informative)
Re:Does XEN have a future? (Score:4, Informative)
KVM only works on systems that support hardware virtualisation. Xen will run unmodified operating systems on these platforms, but also supports paravirtualised guests on older systems (and paravirtualised guests are faster on any hardware). As far as I know, KVM is x86-only, while Xen runs on x86, PowerPC, Itanium and ARM (Samsung are doing some very cool things with Xen on ARM).
There are a few things that Xen supports that KVM doesn't, such as live migration. This is probably the right time for the obligatory plug for my book [amazon.co.uk], if you want to learn more about how Xen works.
Comment removed (Score:4, Informative)
Re:Does XEN have a future? (Score:3, Informative)
Wait, what? KVM supports live migration [qumranet.com], and in fact KVM supports it better than Xen ever did.
Xen allows live migration only between machines with identical or very similar processors. KVM supports live migration between any two systems that can run KVM. For example, if you want to live migrate from an Intel to an AMD host, KVM is your only option. If you want to live migrate a 32-bit guest between a 32-bit host and a 64-bit host, KVM will do that, Xen won't.
Comment removed (Score:3, Informative)