The Book of Xen 88
swsuehr writes "The Book of Xen: A Practical Guide for the System Administrator provides an excellent resource for learning about Xen virtualization. I frequently need to create test environments for examples that appear in various books and magazine articles (in the interest of full disclosure, I've never written for the publisher of this book). In the days before virtualization that meant finding and piecing together hardware. Like many readers, I've been using virtualization in one form or another for several years, including Xen. This book would've saved hours searching around the web looking for tidbits of information and sifting through what works and doesn't work in setting up Xen environments. The authors have done the sifting for me within the ~250 pages of the book. But far beyond, the authors also convey their experience with Xen using walkthroughs, tips, and recommendations for Xen in the real world." Read on for the rest of Steve's review.
The Book of Xen is written with the system administrator in mind; someone who is comfortable with tasks like installing Linux and working with the command line. While it wouldn't be impossible for someone completely new to Linux to accomplish the tasks in the book, a bit of experience would go a long way to both visualize and complete the installation and configuration steps shown in the book. As stated in the introduction, the book is organized "(mostly) alternating between theoretical and practical discussion [because] an admin needs both practical experience and a firm theoretical ground to effectively solve problems..." (xxiii).| The Book of Xen: A Practical Guide for the System Administrator | |
| author | Luke Crawford, Chris Takemura |
| pages | 312 |
| publisher | No Starch Press |
| rating | 9/10 |
| reviewer | Steve Suehring |
| ISBN | 1593271867 |
| summary | A guide for using Xen for virtualization. |
The authors do an excellent job of explaining what Xen is and where it fits in the virtualization landscape. This explanation begins with the introduction where the reader gathers a brief history of virtualization along with Xen's place in the landscape. Xen's limitations and reasons for using Xen are also covered right in the introduction, along with an overview of the book.
Chapter 1 begins with a high-level overview of Xen. This discussion is excellent if only to get the readers on equal footing for the discussions to come later in the book. Included in this chapter is a discussion of various techniques for virtualization including Full Virtualization, OS Virtualization, and Paravirtualization. The section on Paravirtualization leads nicely into some of the underlying details of scheduling, interrupts, and memory, and other resource management which are handled by Xen and discussed later in the chapter.
Chapter 2 sends the reader down the path of installing and using Xen. It's a short chapter, coming in at about 9 pages, and the reader is expected to be able to handle an install of CentOS with just a bit of guidance from the authors on specific options to select. This is a key point for those among us who have a preference for a certain Linux distribution. The book isn't tied specifically to a single distro, as the authors note in the introduction, "[w]e've tried to keep this book as distribution- and version-independent as possible, except in the tutorial sections, where we try to be extremely specific and detailed..." (xxiv). The base or host system upon which the examples run is based on CentOS, which the authors acknowledge and highlight in Chapter 2, "[f]or the purposes of this chapter, we'll assume you're installing CentOS 5.x with the server defaults and using its built-in Xen support. If you're using something else, this chapter will probably still be useful, but you might have to improvise a bit" (13). There is discussion of the Xen-tools package in a later chapter which shows its installation under Debian Linux too. So far from being tied to one distro, the book is refreshingly neutral in this regard.
By the end of Chapter 2, the reader has a working Xen host system and a domain 0 or dom0 host upon which to provision virtual machines. Included in Chapter 3 is a discussion of how to provision guest operating systems, known as domU in Xen-speak. The authors devote a good number of pages to making this task clear, and work through examples of basic domU installation and the use of package management systems and Debian's debootstrap to create domUs. Additionally in Chapter 3 the reader learns how to convert VMware disk images to a format usable by Xen.
Chapters 4 and 5 examine details of the Xen backend, including storage and networking. Chapter 4 stands out for its recommendation of blktap and LVM (Logical Volume Manager) as the storage backend as well as an overview of LVM itself, along with the use of networked storage for Xen.
Chapter 6 looks at tools for management of Xen, focusing on Xen-tools, libvirt, and Xen-shell while Chapter 7 gives advice for hosting untrusted users with Xen. Chapter 8 discusses the use of Xen with Unix-like operating systems and includes sections on Solaris and NetBSD.
The ability to migrate the virtual machine from one physical machine to another is one of the advantages of virtualization. As pointed out by the authors, a virtual machine might be migrated to take advantage of newer hardware, to perform maintenance, or any number of other reasons. Chapter 9 is of interest for its discussion of Xen migration. Cold and Live migrations are examined and Footnote 1 on page 126 is interesting for its reference to the Kemari Project and Project Remus which are projects to add hardware redundancy to Xen.
Tools and techniques for the measurement of Xen performance are shown in Chapter 10, which walks the reader through basic usage of well-known tools such as Bonnie++, httperf, UnixBench, and others. More importantly for the Xen admin is the discussion of Xen-aware profilers like Xenoprof which is "a version of OProfile that has been extended to work as a system-wide profiling tool under Xen..." (151).
Chapter 11 covers the Citrix XenServer, which is the enterprise-grade commercial Xen product from Citrix. The authors summarized it best in the review of Chapter 11: "Can Citrix's product replace the open source Xen? As always, the answer is maybe. It offers significant improvements in management and some interesting new capabilities, but that's balanced against the substantial cost and annoying limitations" (174).
Chapter 12 begins the discussion of Hardware Virtual Machines (HVMs), which are virtualization extensions that enable "an unmodified operating system [to run] as a domU" (176). This means the ability to run an unmodified version of Microsoft Windows as a guest OS within a Xen environment. The HVM discussion in Chapter 12 leads nicely into Chapter 13, "Xen and Windows".
The main chapters of the book end with Chapter 14, "Tips", and Chapter 15, "Troubleshooting". Both chapters draw on the experience of the authors and provide value to the book for their recommendations. Though the tool of choice for troubleshooting is the nearest Google search box, it's still helpful to glance over the content in the Troubleshooting chapter if for no other reason than to maybe remember that it's there when you receive the dreaded "Error: DestroyDevice() takes exactly 3 arguments" error.
The Book of Xen is almost certainly a time-saver for anyone looking to implement Xen or virtualization with Linux. The back cover states "The Complete Guide to Virtualization with Xen". The book lives up to that statement and more.
You can purchase The Book of Xen: A Practical Guide for the System Administrator from amazon.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
They missed their chance! (Score:3, Interesting)
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We felt that Persig puns had been done. (Score:1)
not that I have anything against Persig, but xen/zen puns are pretty worn out. We had a bit of a scare when we noticed that the proof for the rear cover said "Xen and the art of virtualization" - I mean, Our "no persig puns" rule aside, that's what the Cambridge folks called one of the first papers on Xen, so there would have been copyright issues. No starch caught the mistake before it hit paper, though.
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Both of those books should be modded -1 overrated.
Zen and the art of Motorcycle Maintenance (Score:1)
Was recommended to me by someone I respect quite a lot, someone who isn't known for being 'fuzzy headed'
But yeah, I read the book and I didn't get it, either.
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what philosophy do you like? (Score:1)
Personally, after the age of 25 or so, I started to agree more and more with Paul Graham [paulgraham.com] on the subject
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There was one contemplation point in the book that was outside the norm of what you would learn in school: "what is quality?" (define quality).
Prior to reading the book, you probably could not have answered that question. After reading the book, you can. It ties into the opening line of the book: "And what is good, Phaedrus,
and what is not good -- Need we ask anyone to tell us these things?"
Outside of that, it made for an interesting drama.
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That was just "Zen" IIRC, and joined later by the portable "ORAC".
Book of Xen (Score:4, Funny)
Chapter 2: Platforms, the silent killer.
Chapter 3: Giant psychic fetuses and you.
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Does XEN have a future? (Score:1)
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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 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, up
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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.
This is false. You can actually run various BSDs under Xen, and you can run Windows too.
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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.
This is false. You can actually run various BSDs under Xen, and you can run Windows too.
I believe he meant that the hypervisor itself is a forked version of Linux. Sure, you can run any guest OS you want on both Xen and KVM.
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Either way it's still wrong. Dom0 isn't limited to linux, opensolaris and netbsd are also capable of running that hypervisor. Amazon has also been prodding the FreeBSD Foundation to finish their work in Dom0 as well.
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we've got a chaper on running OpenSolaris and NetBSD Dom0s in the book. We got our first taste of Xen, in fact, on NetBSD before moving to Linux Dom0s (we're talking about moving back, now that NetBSD 5 is out with x86_64 and i386PAE support)
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"The hypervisor is linux" is the idea behind KVM. The Xen hypervisor is most certainly not Linux.
Re:Does XEN have a future? (Score:4, Informative)
Disclaimer: I've been a Xen developer in the past and I'm currently obliged to work on Xen-related stuff for my degree.
Minor clarification: Xen support for running as a domU is upstream and there are plans to get dom0 support upstream as well. If getting dom0 support upstream doesn't happen, at least (hopefully) they might be able to base their dom0 kernel on a patchset on top of the kernel.org domU support rather than the horrible forked business they used for a long time :-S
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Isn't dom0 itself a hypervisor kernel? If so I highly doubt Linux will integrate a kernel within itself.
Dom0 isn't actually a hypervisor, no. Xen itself is the true hypervisor on the system and it controls access to the CPU, system memory and various other very low level concerns. Any OS that runs on a Xen system must be a virtual machine of some kind.
Dom0 is a special virtual machine that happens to be allowed to do privileged stuff like accessing the real hardware on the system and managing other domains. Basically you get a dom0-capable kernel by starting from a paravirtualised domU kernel and adding va
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Maybe both diks are twin brothers who frequently disagree with each other but share the same account. Or ol' dikdik may have disassociative identity disorder.
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You must like running dodgy old software. The most recent Xen dom0 that's half-way stable I can find (Debian Lenny) is borderline for my needs (dodgy multipath, creeky mdadm, only 90% ready for recentish hardware (Dell R710)...).
I avoid the Debian port of the SUSE port (Score:1)
of the xen stuff- I've had nothing but trouble with it in testing, and looking, it seems that the debian people aren't particularly interested in helping if you have problems, and if you ask the xen mailing lists, they tell you to ask the debian people. If you want stability, you have to deal with the 2.6.18.8-xen kernel distributed by xen.org, or the 2.6.18-patchedtohellandback kernel distributed by RedHat. (the Suse kernel might be stable, I haven't tried it, but the debian port of the suse kernel that
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No, KVM des it worse and simpler - Xen is faster than KVM on the same hardware (about 10% for disk I/O comparing Xen paravirtualisation with KVM virtio-blk).
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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.
This is quite a misleading assertion. I wrote a book about the Xen internals [amazon.co.uk], so I'm somewhat biased, but you make it sound like KVM is a much simpler approach than Xen. There are a few issues with this.
Xen is a hypervisor. It runs in privileged mode (ring 0 on x86) and is very small. Linux is a kernel ('supervisor') that runs in privileged mode and is massively more complicated than Xen. The confusion comes from the fact that Xen delegates a lot of things to the domain 0 guest. Rather than supportin
Re:Does XEN have a future? (Score:5, Informative)
You make KVM sound like it's nothing more than a desktop virtualization package, as if somehow it's less of a virtualization solution than Xen, and that's just bullshit.
I'm running KVM on Ubuntu 9.10 right now with three guests; Windows Server 2003, an Ubuntu 8.04 install running as a file server and a Debian Lenny install for my webserver. With the newer versions of KVM, I should be able to get a SCSI card running on a guest (paravirtualization), so I'll be giving my backup server a shot as a guest as well.
I'm not trying to claim KVM is better than Xen, but the characterization of KVM that you give might have applied a couple of years ago, but it's just uninformed crapola now.
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KVM does not do paravirtualization, it virtualizes a full x86 processor (with all its overhead)
KVM does not need to do para-virtualization, but it can do para-virtualized I/O to get better performance (see virtio [linux-kvm.org]).
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If by stable you mean Lenny then Xen is the best - Debian's Xen works great on Lenny. If you want to use Squeeze then you have a problem, dom0 doesn't work yet, but it's been promised. After Squeeze you're screwed.
Personally? I would not use the debian Dom0 (Score:1)
DomU works, and should continue to work for the foreseeable future; DomU paravirt ops is upstream, so unless debian goes through extra effort to break xen DomU support, it should Just Work.
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It's worked for pretty much everything I've thrown at it. I haven't tried some of the more complex networking schemes, so I haven't tried building a NAT router. I might play with that at some point in the future, and toss out my existing Linux-based router. Then
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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.
I believe this statement is False. I replaced a bank of servers using Xen. It worked fine, but I needed better driver support and its fork of 2.6.18 or whatever wasn't cutting it.
I switched to KVM two years ago and have had better success than with XEN. On one host right now, I have 8 Windows 2k guests including a SQL Server, Exchange servers, domain controllers and web servers. There are also 4 various flavors of linux servers running.
Using KVM has been a joyous breeze compared to dealing with XEN.
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One of my biggest complaints about KVM is the fact that it requires CPUs which support the HVM CPU capabilities (i.e. Intel's VT or AMD's AMD-V). For a site which has already has hundreds, if not thousands of systems running older P4/Xeon hardware, expecting them, or a small company with fewer systems to upgrade to get newer CPUs which can support KVM is not reasonable. Add this to the whole pile of fecal material surrounding the kernel team not putting the ParaVirtOps code into the kernel tree, and Xen D
Try qemu or virtualbox (Score:2)
Not as quick as with hardware virtualisation and consumes rather too many host cycles, but kqemu in particular is pretty straightforward to set up on older CPUs with rhel or centos (just make sure the kernel module version is compatible with the emulator).
Personally, I don't think that is an issue (Score:1)
if you pay for power, replacing 8 P4s with 1 dual quad-core xeon or opteron usually saves you enough in power costs to pay for the capital cost in a few months.
For me, the big differentiator is robustness and reliability. KVM will get there, I'm sure. But in the hosting space, Xen is the established tool, and KVM is the new technology. Nearly all the linux developers are rooting hard for KVM, which may mean that it will become better. Personally, I'm hedging my bets by learning both. But for now, at
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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.
How is that? They both support full virtualization, and they both support paravirtualization for things like networking and disks (they even use the same protocols for this - virtio). Most of the debate I have seen regarding the two is whether it is better to have a specialized hypervisor (Xen) or use a general purpose, but heavily developed and very much optimized, hypervisor (Linux). The performance benchmarks are six of one and half a dozen of the other so this debate doesn't seem overly relevant.
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.
I'm n
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Redhat et al are doing xen .. I think (corrections please)
Correction: Red Hat aquired Qumranet, the inventors of KVM (link [redhat.com]), so Red Hat is abandoning Xen in favor of KVM as well.
Re:Does XEN have a future? (Score:4, Informative)
Disclaimer: I've been a Xen developer in the past and I'm currently obliged to work on Xen-related stuff for my degree. However, please take the following as my personal opinions!
Wrt keeping pace with kernel driver development: it's worth noting that most of Xen's hardware support comes from running device drivers within a privileged Linux VM (dom0). So most things supported under Linux should work under Xen, plus new drivers should also work as they're added (assuming you're running an up-to-date Linux, which as others have noted you may not be given Xen's officially supported dom0 has mostly been based on 2.6.18, though I hear rumours that proper support for running kernel.org kernels as dom0 might be coming or already available somewhere). That said, stuff like power management / CPU frequency scaling / hibernate / etc tends to need co-operation from Xen, so that can lead to some duplication and extra complexity for Xen to support (I don't know that it does support hibernate support, for instance).
I think that the kernel developers have given Xen support in mainline a fairly rough ride (though as the patches were somewhat large and unusual, that's partly understandable). The Xen developers could probably have handled the merge faster by engaging more and better with the kernel community earlier on.
Regarding distro support - RedHat made Xen a major feature, with good Xen support in RHEL5 (and later support for RHEL4 running as a PV Xen guest) and Fedora. However, relatively early on they started isolating their command-line tools and GUI from the specifics of Xen through an abstraction library called libvirt, a command shell called virsh and a gui called virt-manager. They are now going with KVM as their primary virtualisation feature for the future, with the same UI provided. Obviously they'll have to keep supporting Xen in RHEL due to long term support guarantees. Fedora hasn't supported running as dom0 for a couple of releases as they've decided to stop porting the Xen patches and wait for kernel.org support (they did provide some development and impetus to the mainlining effort, to help this goal along). RedHat has bought the company which wrote KVM and also acquired their SPICE virtual desktop protocol and additions to KVM / Qemu to support this. SPICE is currently most useful for Windows guests from what I've read but it can do some pretty impressive stuff.
SuSE are still quite keen on Xen AFAIK and Xen is certainly still an OSS project which continues to be developed and enhanced. That said, XenSource (which is now owned by Citrix) isn't really in the business of providing virtualisation for Linux distros (although the open source Xen can do that), so much as in selling "appliance-style" virtualisation software a la VMware ESX. They want to be attractive as a commercial virtualisation platform for whatever is expected to be popular in data centres and they're not so worried about being a de-facto standard in Open Source circles.
Oh, you want a nice Xen environment? (Score:1, Offtopic)
Sorry, I just couldn't resist.
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haha. Linode is one of the better providers. they are cheaper than slicehost, but more expensive than I am. According to the latest benchmarks I've seen, though, they beat us all (slicehost, ec2 'small', prgmr.com) in terms of CPU power. (though I'm pretty up front about the fact that I optimize for cheap ram over all else, so the results are unsurprising)
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Isn't everyone like just using KVM? (Score:3, Interesting)
Y'know, there by default vs reinstalling your kernel and patching everything every release etc.
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RedHat is supporting Xen for the lifetime of the RHEL5 spin, which is at least a couple years from now. I think you have until 2014 until they stop supporting Xen.
I was skeptical of the move to KVM but I think it's a good technology. It has some very interesting features that Xen does not, including KSM (kernel same-page merging) and better memory balooning. Plus it makes much better sense from a support standpoint. Xen is owned, at the top, from a proprietary company (Cisco). It was only recently (Oct 20
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Wow - how many inaccuracies can you pack into one comment?!
Xen itself - including not just the hypervisor but the kernel code needed for dom0 and for paravirtualized domU - is GPL licensed, and always has been. What Citrix (NOT Cisco) recently open-sourced was the control stack used in he commercial XenServer. There has always been an open-source control stack -- it has been possible to run a Xen system entirely using GPL licensed code. The only change in October 2009 was to make the management APIs compat
prgmr.com (Score:1, Offtopic)
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By contrast I've never heard of this book, or this guy, but I wrote xen-tools & xen-shell...
You have a short memory (Score:1)
I'm pretty sure I've emailed you to ask dumb questions several times, and you answered. :)
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I'm sorry for my early morning terseness, then!
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Oh my god, that's cute! (Score:1)
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The review needs ... google (Score:3, Insightful)
The review needs to list, what the book has, that a google search will not find for free.
The disadvantage of the book, is the review makes it sound like an edited, slightly out of date collection of FAQ printouts, and it costs money.
The advantage of the book, is ... Come on, give me a reason to buy the book. I got money burning a hole in my pocket here.
Here are reasons why I'd buy a book that covers a "google-y" topic. First of all, if the $$$ went to a foundation that paid the program authors, or some charity (EFF?). Maybe if it had diagrams and flowcharts or other graphical aids you can't find via google. Maybe if it had interesting exclusive content, behind the scenes interviews with the authors, candid explanations of why and how it was designed the way it was, that simply cannot be found on the internet. Maybe if it had workbook like qualities, like planning worksheets to plan and organize your deployment. Maybe if it had textbook like qualities like questions at the end of each chapter with an answer key at the end. Maybe if it was an artistically beautiful collection of "stuff" like XKCD cartoons, FAQs, stories, pictures, poems, all tied to a common theme in an aesthetically pleasing manner.
Thats what I want to see in a slashdot review of a "google-y" topic.
half what you are talking about is (Score:1)
'desktop virtualization' which is another animal entirely. (personally, I think desktop virtualization will suffer the same fate of other recent 'thin client' schemes, but really, it's not my area, so that's just wild speculation.)
Provisioning and mass deployments is something I go into a little bit... but certainly isn't the focus of the book. I firmly believe that it is madness to treat physical and virtual servers differently; you want to use one tool for both. And right now, the best one tool is c
If I may (Score:1)
books can't really compete as references anymore, I don't think. The advantage of a book is that it's easier to sit down and read a book cover to cover than to figure out what you need to look up in order to get an overview of a technology.
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The review needs to list, what the book has, that a google search will not find for free.
Off the top of my head, I'd go with coherency, structure, and a lack of insults.
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The review needs to list, what the book has, that a google search will not find for free.
Off the top of my head, I'd go with coherency, structure, and a lack of insults.
Sounds just like a FAQ... which google will find for free
Google Xen FAQ first link for me was
http://wiki.xensource.com/xenwiki/XenFaq [xensource.com]
Good coherency, although it was not, it looks like it was written in one sitting by one guy, or at least edited to look that way.
Good structure, its an outline, and the outline even looks well designed.
Lack of insults, well, its no mailing list. And for $20 or whatever the book costs, I'll glance over a mailing list post calling some dude a noob, or whatever.
XEN has a way to go yet (Score:1)
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hah. being familiar with linux, and not so familiar with Windows, I had the opposite problem. Xen networking is... Linux networking. (the big problem is that the Dom0 kernel is crusty and ancient; something that should be remedied with Xen 4, which should be out Real Soon Now.)
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yeah, they went over the 'citrix xen' chapter.
But what I was trying to say is that networking under xen is pretty easy for me, as it's just Linux stuff. The times I've had to deal with vmware for clients, I've been frustrated trying to do what I wanted to do with their interface, something obviously designed for windows users. I'm not saying the vmware interface is bad; just that it was designed for a windows user.
Something completely off topic (Score:2)
- or nearly:
This book title is a wordplay on "Zen", obviously; which leads me, once again, to wonder why the hell English speakers think that "X" is pronounced "Z"? Is it just mental laziness? The depravity that inevitably comes with the filthy excesses of Capitalism? A conspiracy by the religious right?
In my experience "x" is pronounced "ks", as demonstrated in a word like "sex" - you don't pronounce it "sez" unless you've had a few pints more than what is good for you, in which case sex is probably irrele
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Describing it as laziness could be considered a bit of a faux pas.
Hey, I hope that the general tone of my post would be a hint of its entirely humorous intent. I have never heard any good explanation of why "X" ahould be pronounced "Z" when it stands first in syllable, that's all; being a Danish speaker, I am no stranger to pronouncing chains of consonants, so it puzzles me that Enhlish speakers seem to go to such lengths to avoid it, by inserting vowels or even changing the consonants completely.
Errata available! (Score:1)