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Running Xen 98

Posted by samzenpus
from the read-all-about-it dept.
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.
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
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 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.
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Running Xen

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  • by Anonymous Coward on Monday June 09, 2008 @03:35PM (#23714179)
    ... I don't think the results were favorable.
  • by XorNand (517466) * on Monday June 09, 2008 @03:36PM (#23714197)
    I don't know why I keeping reading /. book reviews; I never feel like I get much information in exchange for my two minutes. Who is the target audience of this book? What kind of Xen experience did the reviewer have prior to picking up this book? What did he actually learn when he was finished with it? There's too much verbiage attributed to how he "felt" about the book or the style it was written in and not enough hard information.

    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: (Score:1, Insightful)

      Not only that, but you'd think the slashdot comments would refer to the book, which is the topic of the post, but instead you get comments regarding the technical subject of the book.

      Rarely would you ever read a counter point to the reviewer such as, "In my opinion, the book offered X..."
    • by Lord Apathy (584315) on Monday June 09, 2008 @03:58PM (#23714569)

      Does it tell me how to fix my fucking motorcycle?

    • by kiehlster (844523)
      At least it wasn't a blatant /vertisement, but I have to agree, this was useless and maybe obvious. My impression makes me believe this is no more than a rehash of the installation guide and some first-hand suggestion. It sort of rings, "If you need the install guide written in easier to follow English, this guide is highly recommended."
    • by bwhaley (410361)
      I don't know why I keeping [sic] reading /. comments. I never feel like I get much information for my 30 seconds. What is this uber-useful xen mailing list? There's too much whining about how people "feel" about the article but no meat.
    • Actually, the information about the networking chapter made me much more interested in getting and reading this book. The reviewer may not have cared much, nor does XorNand, but the second time I set up Xen was a server for a startup, and I really needed more information in a hurry about networking. Hope the rest of the book is as detailed...
    • by stry_cat (558859)

      I don't know why I keeping reading /. book reviews; I never feel like I get much information in exchange for my two minutes.

      I must agree on this. While certainly any review should tell us how the reviewer "felt" about the book, there needs to be some hard facts too.

      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.

      Very similar to my experience. The HowTo over as xensource was quite adequate.

      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.

      Now here is where I disagree. Most of my questions go unanswered or if I do get a reply it is more like the blind leading the blind. What I've read on the list indicates that the folks are more friendly and helpful than the typical opensource list. So I suspect my questions are just g

  • by Anonymous Coward on Monday June 09, 2008 @03:52PM (#23714467)
    Haven't the kernel developers basically given xen the cold shoulder, preferring now to dedicate their efforts to kvm, the virtualization solution which is now part of the mainline kernel? The problem, from what I recall from reading some threads on the subject a while back was that xen needs to keep pace w/ kernel driver development work, which is an extra effort for the developers. It's easier for them with kvm since it's part of their dev tree. Right now I think Ubuntu is the only big distributer shipping kvm; Redhat et al are doing xen .. I think (corrections please). On that count, xen is doing well. But moving forward, it seems like they have to do a lot of extra work to track kernel development, which will be made harder by virtue of the fact that key kernel developers may not feel like devoting time to what they feel is a duplicate effort.
    • by squiggleslash (241428) on Monday June 09, 2008 @04:47PM (#23715359) Homepage Journal

      Xen and KVM are completely different types of virtualization solution. The supposed rivalry between the two is largely bad journalism, not rooted in anything to do with the platforms themselves.

      If you want to run a single physical computer with multiple operating system instances, such as replacing a bank of servers with a single machine, Xen is your guy. If you want to run VMs under Linux, KVM is your friend. Conflating the two is like comparing... well, to use a car analogy, for this is Slashdot, a railroad with a tractor trailer.

      • Car analogies are all well and good.... but can we have some detail on that.

        And where does virtualbox fit in with all this?

        • I can't expand on it here because Pudge thinks that 4k is a really big message, and I really can't be bothered any more to navigate through the unholy fuck-up that is Slashcode today.

          However, I did write something on Multiply that essentially explains the whole issue. [multiply.com] If you understand why KVM and Xen are entirely different explanations, you understand why a desktop system like Ubuntu was never going to "choose" Xen as a "virtualization solution", and probably shouldn't have even considered it back when

          • I'm actively researching the whole area with a view to rolling the "run a windows app on an ubuntu desktop" scenario out to a collection of colleagues.

            An interesting counterpoint to what you're saying is coming from Ulrich Drepper [livejournal.com] the libc guy.

            • Re: (Score:3, Informative)

              by squiggleslash (241428)

              Counterpoint? Drepper's not explaining that the "KVM and Xen are competitors" war is valid, he's just buying into it without justifying it. He doesn't "get" Xen so he assumes it's used in the same areas as KVM and that, therefore, crude performance comparisons are valid. I've not really read much of his stuff before, so it'd be inaccurate to say I've lost respect for the guy on reading that article, but it does sound like he's "not getting it" which reflects somewhat poorly on him. I know I made the right

              • Sorry to so try your patience.... but I've reread your multiply.com article _and_ Dreppers two and I'm still grasping for a good statement along the lines...

                When I want to do XXX then Xen is better than Kvm because this aspect of XXX demands YYY which Xen not Kvm provides.

                Currently I'm guessing XXX is "I am an Colocation / ISP and want run a bunch of OS instances so that it effectively appears to my customers that they are the only one using this server, but actually are sharing the cost of the hardware

      • Re: (Score:3, Informative)

        by segedunum (883035)

        Xen and KVM are completely different types of virtualization solution.

        Well yes they do do things differently, but KVM does it better and simpler by just running on Linux as the base system hypervisor. From a maintenance point of view things get far simpler, as the OP said.

        If you want to run a single physical computer with multiple operating system instances, such as replacing a bank of servers with a single machine, Xen is your guy. If you want to run VMs under Linux, KVM is your friend.

        That statement is

        • I think the difference GP is trying to point out is that Xen is targeted more for the VMWare ESX market - the dom0 OS can (and should) be as stripped down as possible - whereas KVM is (currently) more targeted for the VMWare Workstation or QEMU market of bolting a VM onto an existing general-purpose system. That could change on both counts, and kvm developers have stated that they intend it to be general purpose, so there's really no reason that Xen could not be ported to kvm, as it were.
          • by jdowland (764773)
            The vmware esx bare-bones OS is as Linux derivative. So it's more like KVM in that regard than Xen.

            Afaik, the *real* difference is KVM does no paravirtualisation, it is purely a kernel interface to the VT extensions on newer x86 chips. So it's "cleaner", but is no use if you don't have the VT extensions.
        • by TheRaven64 (641858) on Tuesday June 10, 2008 @09:12AM (#23724191) Journal

          You're implying that Xen can't run VMs under Linux but KVM can, or Xen can run VMs on systems other than Linux or something that KVM can't do? They're both Linux only at this point, and Xen effectively runs a forked version of Linux because it isn't, and won't be, upstream.
          Xen is a hypervisor. It runs under Linux, not on top (although the Xen devs do often run Xen in KVM for development). It uses one or more slightly (or very, depending on your hardware) privileged guests to provide drivers. These can be Linux, NetBSD or Solaris.

          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.

          • Re: (Score:3, Informative)

            by David Jao (2759)

            There are a few things that Xen supports that KVM doesn't, such as live migration.

            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.

          • by segedunum (883035)

            Xen is a hypervisor. It runs under Linux, not on top
            Yes, I know. That's the maintenance problem the OP is pointing out, and its future development doesn't look as great as KVM's does outside of the kernel.
            • Linux is completely irrelevant to Xen. Xen runs quite happily with a NetBSD or Solaris domain 0. It has no dependency on Linux. In a particular configuration, it might have a dependency on a driver only available for Linux, but that is all.
              • by segedunum (883035)

                Linux is completely irrelevant to Xen.
                It requires a patched Linux, or another OS, to provide its device support, which is completely pointless. Same difference.
        • by squiggleslash (241428) on Tuesday June 10, 2008 @10:00AM (#23725055) Homepage Journal

          Well yes they do do things differently, but KVM does it better and simpler by just running on Linux as the base system hypervisor. From a maintenance point of view things get far simpler, as the OP said.

          Sure, and Wifi does it better and simpler than Bluetooth by using Ethernet frames (The Bluetooth vs Wifi "war" is also a good example of where geeks get it completely, 100%, wrong by not recognizing the entirely different applications the technologies are aimed at.) You're comparing apples to oranges, and assuming that because KVM works better in a specific scenario that it works better.

          That statement is just, well, daft. You're implying that Xen can't run VMs under Linux but KVM can, or Xen can run VMs on systems other than Linux or something that KVM can't do? They're both Linux only at this point, and Xen effectively runs a forked version of Linux because it isn't, and won't be, upstream

          It's not daft, your response makes no sense. Let's break it down:

          You're implying that Xen can't run VMs under Linux but KVM can

          That's right. Xen cannot run VMs under Linux. Xen runs VMs on the bare hardware. In the Xen environment, operating systems run under Xen, not vice versa. The only way to run Xen "under" Linux is to run it in an emulator!

          or Xen can run VMs on systems other than Linux or something that KVM can't do?

          This sentence makes no sense as is. It can't run VMs under Linux, as stated above. In terms of operating system support, you can run various operating systems under Xen as "dom0". Dom0 is a special domain that most hardware is managed by by default (though you can redirect any almost piece of hardware to be managed by any guest system. For example, on my home server, one of the Ethernet cards is managed completely by a domU.) Dom0 can be one of many operating systems, including Linux-based systems, OpenSolaris/SunOS, OpenBSD, NetBSD, and certain versions of FreeBSD (with certain versions of Xen.) The only restrictions that go with being dom0 have to do with the kernels for those systems being Xen-aware.

          This flexibility brings enormous advantages incidentally. With enough memory, you can install something like Solaris as your domU and have it export NFS shares upon a ZFS file system to all of the domUs, giving every operating system you run the advantages of the host. At the other extreme, you can install something small and light - bugs aside, I found Xen's integration with Ubuntu Server 8.04 LTS wonderful when setting up my little firewall-gateway/servers box. I have the barest Ubuntu Server installation (no X11/GNOME/etc) as dom0, and even barer systems for the domUs It's great.

          They're both Linux only at this point, and Xen effectively runs a forked version of Linux because it isn't, and won't be, upstream.

          Xen is PowerPC, ix86, and AMD64 at the moment. In terms of operating systems it can run as dom0, see above. In terms of operating systems it can run as domU, well, the choice is massive.

          Really, what you're saying convinces me you haven't really investigated what makes Xen Xen. I would never install Xen on my laptop. I'd never install KVM on my server machine. Take another look at both, and see why their strengths make them suitable for different purposes, neither are solutions that fit every application, and they complement each other well in terms of the applications they efficiently support.

          • by segedunum (883035)

            You're comparing apples to oranges, and assuming that because KVM works better in a specific scenario that it works better.

            Hmmmmm, no. They're both virtualisation technologies, and the point is KVM's future looks a hell of a lot better as part of the kernel than Xen's outside of it. Nice try though.

            Xen runs VMs on the bare hardware. In the Xen environment, operating systems run under Xen, not vice versa. The only way to run Xen "under" Linux is to run it in an emulator!

            Yep. There's the problem being descr

      • for this is Slashdot, a railroad with a tractor trailer


        http://www.qstation.org/BNSF_Triple_Crown/ [qstation.org]

        http://www.deluxeinnovations.com/rolling/rollingwnc01.html [deluxeinnovations.com]

        ...you were saying?
    • Red Hat is now pushing KVM, see http://ovirt.org/ [ovirt.org]
      • by Znork (31774)
        As far as I can tell, Redhat is pushing libvirt, which is vm agnostic (you're supposed to be able to use it to manage whatever virtualization tech you want to use).

        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).
        • by Quikah (14419)
          What loads are these that Xen is significantly faster than ESX? All of my testing has seen same or slower performance.
          • On CPU bound workloads, especially any CPU bound task that is "SMP aware", Xen leaves ESX in the dust, especially when using 2, 3 or 4 virtual CPUs. I'm not talking percentage points here, I'm talking Xen simply *smokes* ESX. I run both Xen and ESX at work on current enterprise grade hardware, and for Linux hosts at least, there's just no comparison.

            My experience with ESX is that adding virtual CPUs buys you very little (it's almost a complete waste), whereas with Xen, the performance scales nearly perf
            • by Quikah (14419)
              CPU bound workloads such as? I have never experienced anything like you described.
            • by swb (14022)
              In ESX class, we were told (and this is a gross paraphrasing from something the instructor mentioned off the cuff 6 months ago) that multiple virtual CPUs helps most with VMs that run a lot of monolithic processes, as the ESX CPU scheduler is biased towards running on whatever CPU is available, which apparently can hammer cache coherency for SMP-aware multithreading. I think he said that setting processor affinities helps, but can hurt in other ways as well as being incompatible with VMotion.

              I think that a
            • by loki-yo (730813)

              On CPU bound workloads, especially any CPU bound task that is "SMP aware"

              The immense majority of real life task are not CPU bound anymore with current multi-core CPUS, but RAM and IO bound.
            • by Znork (31774)
              On the management front, nothing touches Virtual Center, not even close...

              Unless you're using Linux desktops. I've seen rumors about the VIC client coming to linux, but after, what, three, four years of customers asking for it? From the point of view of virtualizing linux, the lack of interest in supporting Linux has pretty much negated the advantages of virtual center.

              In the long run, a lot of what virtual center does isn't that hard to replicate with standard linux infrastructure (HA, resource management,
          • by Znork (31774)
            Are you testing paravirtualization or hardware assisted full virtualization? (I'm talking about paravirtualized, the full virtualization would match your experience)

            Examples; iterative shell scripts (ie, anything with lots of forks and execs) had a huge difference. IO performance varied, but xen tended to be significantly faster on anything read-related. Kernel compilations on multiple virtual machines, fair amount of difference. CPU bound, slight but measurable difference.
        • Re: (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 de

          • by Znork (31774)
            paravirtualizes all the hardware and gives you almost all the benefit.

            Have you tested it/what performance levels does it have? It's been a bit too immature to push in the corporate setting yet, but it would be interesting to see if it's getting comparable performance now.

            Xen dropped the ball by not working closely with the Linux kernel developers

            Oh, I agree, duplicating kernel work in the hypervisor is idiotic and a long term dead end, wether it's vmware or xensource doing it.

            so the future for Linux & X
    • by pmgst17 (524425)

      Right now I think Ubuntu is the only big distributer shipping kvm; Redhat et al are doing xen .. I think (corrections please).

      Fedora 9 has kvm, qemu, and xen.

      What's amusing is how David loves on Ubuntu, and fails to mention RHEL / Fedora.
      "Popular third-party distrobutions such as Ubuntu, Gentoo, CentOS, and OpenSUSE were covered; "
      (OK, so CentOS was mentioned, but not RHEL),

      "The popular distros were covered again (Ubuntu, Gentoo, etc.), but this time a twist was added to the mix"

    • Re: (Score:3, Interesting)

      by jandersen (462034)

      Haven't the kernel developers basically given xen the cold shoulder, ...?

      They may have, but I think Xen still has a future - just take a look at Oracle VM. Oracle is a substantial player in the marketplace, whatever else one may think of them, so Xen does have some serious backing. Oracle VM is, as far as I can see, little more than a basic Linux with Xen - "perfect for running Oracle Unbreakable Linux" :-) I've tried it, though, and it works well.

    • by David Jao (2759) <djao@dominia.org> on Tuesday June 10, 2008 @03:55AM (#23721439) Homepage
      Xen has pretty much no support for laptops. Unfortunately for Xen, it's becoming pretty clear that laptops are the future as far as general purpose computing goes. So I would say that Xen has no future.

      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.

      • Xen has pretty much no support for laptops. Unfortunately for Xen, it's becoming pretty clear that laptops are the future as far as general purpose computing goes. So I would say that Xen has no future

        Here's a rewording that I think is more appropriate: Xen has sub-optimal support for laptops. As laptops appear to be the future as far as personal computing goes, Xen has little future in that area.

        But it never did. Xen was never the optimal solution for desktops. Desktop users generally have no desire to

        • Re: (Score:3, Insightful)

          by David Jao (2759)
          First of all, I'm not fighting a war here. I'm just saying nature will take its course, and there is nothing you or I can do to stop it.

          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 hypervi

          • by Bryan Ischo (893)
            But is ACPI support *really* that hard that Xen can't implement it? I don't know the ACPI system at all, but I have to say I doubt it. I would think that managing multiple virtual OS installations is a difficult challenge, and if the Xen team could implement that, would ACPI really present that much of a challenge?
    • Re: (Score:3, Insightful)

      by PetoskeyGuy (648788)
      Amazon EC2 is the largest installation of XEN servers I'm aware of. You can sign up right now and start up to 20 virtual machines for $.10 US per hour. There are some major services built on top of EC2. I would assume Amazon itself uses the technology to run their own services - that should provide a pretty good shelf life and development cycle.
  • I run various operating systems under Parallels and QEMU on my OS X MacBook Pro. But I'm looking to build a fairly high-end Linux box that I'd like to run Xen on. Is there a way I could transfer my existing guests to Xen?

    No doubt I could figure it out somehow, but a FM to R would sure be nice.

    It turns out that you can't boot the BeOS 5 Pro CD under either Parallels or QEMU; the boot loader can't find the kernel, possibly because it accesses the CD drive in a different way than most other operating sys

    • by Znork (31774)
      Easiest way I've seen to do it is to install a -xen kernel in the machine you're about to move, then dd a copy into a file or block device you're planning to use. That works fairly well on fedora/centos paravirtualized hosts on fedora/centos at least.

      Another way is to define an external xen-aware vmlinuz and initrd in the vm config file, in which case you should be able to boot pretty much any linux filesystem (provided the initrd does the appropriate things, of course).

      Cant say how easy it is with fully vi
  • If you'll excuse my off-topicness for a moment here, I can't be the only one who was thinking "Wait, someone actually wrote a serious book about Half-Life?" when clicking onto this...
  • Seeing how Fedora basically spearheaded development of Xen, including it since Fedora Core 4, I find it hard to believe that there's no mention of it.


  • In order to increase the relevance of this book review to the slashdot readership, it would be helpful to include in the summary a definition of what Xen (or the book's technological focus) is. I skimmed the book review and still couldn't find a definition of Xen- I wanted to know if it was a free, open source virtual machine emulator. It is [xen.org]. I am not dissing this review. Just trying to provide feedback to this reviewer so the next review can be written to draw more people into reading and learning about t
  • I've deployed xen at work. It has its issues. A report on these would be much more useful to the slashdot crowd than a book full of information thats largely out of date the moment its published so here goes:

    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

  • by RobNich (85522) * on Monday June 09, 2008 @08:29PM (#23718001) Homepage
    The book HAS to be better than the documentation that RedHat provides for RHEL 5 Virtualization [redhat.com]. It ranks among the worst-written, most useless documents I've read in a long time.
    • by corbettw (214229)

      It ranks among the worst-written, most useless documents I've read in a long time.
      You haven't read any of the numerous court orders my ex-wife feels free to continue ignoring.
    • It's been completely rewritten from scratch for the recently released RHEL 5.2. Not sure why it's not on the site yet, but I imagine it will be soon.

      Rich.

    • by jdowland (764773)
      I find most RH docs a lot like that unfortunately. I find it quite incredible that it's often easier to find multiple pages explaining how to use the (self explanatory) redhat GUI admin tools but much harder to find documentation for config file syntax and the like.
  • xm destroy ./

    xm create ./

    And hey presto, it's back!

  • 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.

    You know, I can't agree with you there, on account of my being an IT professional evaluating xen for a mid-sized to en

  • Stashed under the pilot's seat aboard the Liberator?

fortune: not found

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