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.
Another near-useless book review. (Score:5, Insightful)
In my personal experience, Xen isn't that hard to get working. I think I read a single HOWTO and was up and running in an afternoon. I subscribe to the mailing list which is a great resource for the more arcane problems (passing a PCI telephony card to an Asterisk domU, for instance). The developers and veterans are very patient and quite helpful. I was hoping this review would tell me why I should or should not spend money on another Xen resource. Since I feel like I still don't know anything about the book, it has failed to do so.
Re:Another near-useless book review. (Score:1, Insightful)
Rarely would you ever read a counter point to the reviewer such as, "In my opinion, the book offered X..."
Re:Does XEN have a future? (Score:4, Insightful)
The problem (and it is a showstopper) is that Xen has no ability to perform power management. Even worse, the design of Xen makes it almost impossible to support power management in any sane way. In Xen, every OS on your system runs in a virtual machine. Even the so-called "host" OS, which has special privileges for hardware access, runs in a virtual machine. The actual host kernel is a bare-bones hypervisor with so few features that it cannot be called a full-blown OS.
Power management is very difficult to do under the Xen architecture, because ACPI [wikipedia.org] power management requires all of the power management code to run in the OS. Now, an OS running inside a VM has no ability to monitor power usage for other VMs -- that's the whole point of a VM, after all. So, under the Xen design, the power management code cannot run in the "host" OS. It has to run in the hypervisor.
However, power management is complicated enough, and involves enough dependencies, that by the time your hypervisor has implemented power management, it is already bloated and featureful enough to constitute a full-blown OS. Therein lies the problem: a full-blown OS is very difficult to develop in this day and age, and in order to succeed you need a large team. If you screw up, then the resulting product is fragile and unstable, and nobody wants that. Xen is a very small team compared to Microsoft, or Linux, or even FreeBSD. They have no chance to develop an OS on their own.
One might be tempted to implement some sort of passthrough design where the hypervisor piggybacks off of the power management code in the "host" OS, but such a design requires forking the "host" OS and still involves almost as much hypervisor bloat as implementing power management itself.
In short, KVM is the future, at least for regular users like you and me. KVM has no problems with power management, because under KVM the actual host kernel is the exact same Linux kernel that you normally use, with a complete ACPI implementation. Xen might have a place when it comes to big iron and server rooms, but history shows that very few technologies can survive in server-only space when there is mass-market competition (Itanium anyone?).
In fact, with the soaring cost of energy these days, power consumption is becoming a huge issue even on servers, so it's fair to say that Xen's days are numbered even in the server space unless they drastically change their design.
Re:Does XEN have a future? (Score:3, Insightful)
KVM will scale up to the server space. There is no technical reason why KVM requires "running everything as VMs on a desktop", even though that happens to be required today. In fact I guarantee you that one day KVM will be viable in the server arena. Once that happens, Xen is dead.
By contrast, Xen can never scale down to laptop or even desktop users, because the hypervisor design imposes unacceptable usage constraints for such users.
I said before, and I'll say again, it is very hard for any server-only computing technology to compete against mainstream alternatives. Admittedly, it is easier in the case of software (e.g. Oracle) than hardware (e.g. x86). However, x86 virtualization happens to be moving in the direction of hardware. All of these factors weigh against the hypervisor design. Incidentally, all of Xen's competitors, including VMware and Microsoft, offer at least some virtualization products not based on hypervisors. Xen is the only company tethered to hypervisors, and that does not bode well for them.
You say yourself that "people will try to force fit one solution to the other's area" but then you dismiss this as a non-issue. I think it is a bigger issue than you realize. For example, the reviewer of this book, among all people, complains several times in this review that the book is overkill for what he needs. It looks like he would be better served by KVM. If there is a "war" to be fought, then the goal must be to educate readers about the pros and cons of each option, so that they can choose intelligently. That's all I'm trying to do.
Re:Does XEN have a future? (Score:3, Insightful)