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I would like to deploy Xen virtualization, however I definately not sure which way to go.

Citrix Xen Server has (AFAIK) better managment tools, but does not provide software raid.

Ubuntu / CentOS has Xen installations and support software RAID.

Is it worth to go and buy HW RAID or just stick with SW RAID and Xen budnled with linux distribution.

Which way would you suggest? Are there any other things I should consider?

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8 Answers 8

I'm running Debian with software RAID1 and LVM as XEN dom0 without any problems for some time now. Installing new domU's couldn't be easier with xen-tools, and plain "xm" gives me all the management power I need. Based on my experience, I suggest you save some money and go software raid + your linux distro of choice.

As for SW raid vs HW raid, there's already a great discussion on serverfault: http://serverfault.com/questions/214/raid-software-vs-hardware

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This isn't really an answer to your question as it's a bit subjective and depends on your comfort level with the technologies involved. But here are a few things to think about.

If you need to be able to do live migration then I think this becomes more a mute point. To support live migration you'll need some sort of shared storage that all the XEN host machines can see. You can use NFS or iSCSI for this.

Both Ubuntu and RedHat/CentOS are unfortunately currently moving towards KVM. Ubuntu's support for Xen as a Dom0 has been phased out in the newest version of Ubuntu Server in favor of KVM and CentOS's Xen is behind the Xen development by a couple of versions. Both OS's have decent support for running as a DomU.

That said currently our virtualization is done on Xen running on CentOS and it works well. Although I would love to have a few of the features available in the newer versions of Xen.

I know of a lot of people in the Xen community are running Dom0's in Debian and Gentoo as well so there are other choices. A lot of people will compile their own Xen kernels rather than use the ones from their distro's as well to stay in step with Xen's development.

The beauty of virtualization is that you can try different Xen hosts and figure out what works best for you without necessarily having to do anything to the guests. However if you're using file based DomU's I do believe that Xen Server uses VHD image format by default where the open source version uses raw image files and qcow files. So some care needs to be taken when picking a format to use for your images. There are utilities that can convert between these formats out there as well.

EDIT: After doing some reading it does appear that Ubuntu has decent support for Xen still. Xen 3.3 hypervisor and Xen kernels are in the repository. For more info see https://help.ubuntu.com/community/Xen

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Where are you getting your info that RedHat/CentOS are phasing out Xen for KVM? RHEL5 comes with Xen and they've released recent updates to RHEL4 to provide Xen support. It's a little old (3.0.3) but that doesn't surprise me given how long it takes for updates to come out from RedHat. –  Jeremy Bouse Jul 1 '09 at 20:51
    
RedHat purchased the company behind KVM late last year and they have been pretty clear about the direction that they are going with virtualization. They of course aren't going to drop support for Xen overnight. Here's a good article on this with many quotes from Navin Thadani, senior director of Red Hat's virtualization business. internetnews.com/software/article.php/3806136/… –  3dinfluence Jul 1 '09 at 23:08
    
Here's another good blog post on the direction of virutalization in RHEL that was written today about the 5.4 beta. blog.internetnews.com/skerner/2009/07/… –  3dinfluence Jul 2 '09 at 0:16

Debian 6.0 Squeeze ships with Xen 4.0.1.

The introduction of pvops to the linux kernel solves some issues that led to distros like Ubuntu dropping support for Xen dom0.

Virtual host providers like Amazon are still using Xen and I think we'll see a revival in its popularity.

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Personally I wasn't impressed with the management tools available in XenServer and would much prefer the customizability that's possible with a full blown Linux distribution. Of course, this depends entirely on your comfort level.

As far as software vs. hardware RAID, I think it really depends on what kind of RAID you are doing. I think software RAID is more flexible and in my experience has worked extremely well in a RAID1 or RAID0 configuration.

I'd be more hesitant to use software RAID in a RAID 5 or RAID 6 because both of those configurations rely on a battery-backed cache to achieve suitable performance and data integrity.

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The options for deploying Xen have increased and are continuing to improve. First, one important consideration is the Xen Cloud Platform (XCP), which is an open source version of Citrix XenServer. XCP is "enterprise-ready server virtualization and cloud computing platform, delivering the Xen Hypervisor with support for a range of guest operating systems including Windows® and Linux® network and storage support, management tools in a single, tested installable image, which is also called XCP appliance." (For details see: http://xen.org/products/cloudxen.html)

The Xen management domain has also been integrated into the mainline Linux kernel and distro support for Xen is improving Ubuntu 11.10 and Fedora 15 ( http://blog.xen.org/index.php/2011/09/14/fedora-16-virtualization-test-day/ ) are adding distro support for Xen.

As a middle ground to both of these options (on that let's you get the enterprise features of XCP/XenServer and let's you have a custom Linux platform) is Project Kronos ( http://blog.xen.org/index.php/2011/07/22/project-kronos/)

So there are great options and the options are only getting better.

See also: http://wiki.xensource.com/xenwiki/XCP/XenServer_Feature_Matrix

http://blog.xen.org/index.php/2011/06/14/linux-3-0-how-did-we-get-initial-domain-dom0-support-there/

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This answer was most helpful to me, but still seems dated. Any updates? –  sage Aug 10 at 18:04

I'm using RHEL 5.X with following rpm

http://www.convirture.com/downloads.html u can check this out RHEL next update. To manage all GUI base VM..

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I'd think again about Xen. Aside from Citrix (who clearly have a vested interest) Xen is on a slide into obscurity and back to the computer science community. I use Xen (with a linux Dom0) a lot and have done for a long time, it solved a problem and offered an alternative to VMware. RedHat (and others) are dropping Xen, although they will support it until it's EOL. KVM is the winner in all this thanks to it being in the kernel and RedHat buying the company and having big plans for it.

Unless you're planning on being tied in by Citrix, you should steer clear. At least with the open source xen you're likely to able to migrate to KVM when the time comes with a lot less hassle.

In a few years time KVM, VMware and Hyper-V are likely to be the only real players left on the server. So starting out with Xen now is likely to cost you a lot of time in future.

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Suggesting that Xen is any more proprietary than Redhat owned KVM or VMware owned VMware is a bit silly. –  Dan Carley Jun 29 '09 at 15:44
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The Xen hypervisor is GPL2, I didn't suggest otherwise. Xen Server is a product by Citrix that includes the Xen hypervisor, with proprietary extensions and management tools. KVM is not proprietary either, it's in the mainline kernel and is also under GPL2. RedHat do not own KVM. They do have the extra bits from the purchase of Qumranet that they will use to their commercial advantage. –  goo Jun 29 '09 at 21:49
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To be fair, FLOSS deployments of Xen should see a resurgence once the dom0 pv_ops code gets in the mainline kernel (looking like 2.6.31 or 2.6.32 timeframe) which will make it significantly easier to deploy the latest releases of the Xen userland. –  Ophidian Jul 1 '09 at 21:23
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My point was, that GPL or not, every single hypervisor is being steered by a major commercial vendor. Regardless of your personal preference they all have vested interests. –  Dan Carley Jul 6 '09 at 9:34
    
It's comical to read this five years later - turned out not to be such a slide, it seems... –  sage Aug 10 at 17:38

The answers in this post have grown dated. Although more recent, my answer is a summary from barely skimming the surface of this topic. Hopefully it will jumpstart updates to the thread and I have marked it Community Wiki in hopes that it evolves to better content.

XCP -> XenServer

As I have dug into this, I am increasingly finding that what was XCP has become the open source XenServer, as described at the Xen Project FAQ on this topic. Having now installed the Xen hypervisor twice, I'll test out the XenServer iso, which sounds like it may be the better comparison for most users (although I'm pretty happy with the bare hypervisor).

VMware

I have been interacting with systems hosted by a group I work with where they migrated in the last few years from VMware's free vSphere/ESXi to the commercial ESXi with vCenter. I have been helping them rehost servers into VMware run appliances. I have been impressed with the usability of the VMware solution and I see that this is attractive to the administrator, but there is a price tag for the enhanced feature set.

Having learned more about the free intro version, I am tempted to install that and see how user friendly it is, as I have one group that is familiar with Desktop VMware, but seems wary of server VMs, and this might be a good starter system for them.

Xen Project (hypervisor only)

To test out the Xen hypervisor, I went over to the Weird Stuff Warehouse, bought a used Dell rack-mounted server, and installed Xen (Xen Project, not Citrix). I primarily followed the Xen Project Beginners GUide and used the debian.org instructions as a reference. I stopped at the end of the PV (Paravirtualized) Guest instructions and I initially created three guests -- all Debian. For the lightweight servers I have in mind, Xen-based PV guests seem easy and more than adequate.

I originally planned to back up the VMs and then attempt to migrate the entire server setup to SW RAID (I found instructions at http://wiki.kartbuilding.net/index.php/RAID_1_and_Xen_(dom0)), but now I'm leaning toward testing out XenServer and/or VMware free products (open source in case of XenServer).

Experimenting

If you have a representative system, some time, and you enjoy experimenting, then try out a few of the free options. The hardest thing for me so far was locating USB media I could format - ended up using a spare SD from my phone with a reader - and finding the instructions for loading an iso onto USB media (Ubuntu has instructions for Ubuntu, Mac, and Windows.)

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