<p>Modern Xen is much better. Both Dom0 and DomU are in the mainline kernel, and so no custom kernels are needed anymore. Am using it with Xen 4 on Debian 6 for about a dozen VMs. </p>
<p>The only problem with the distribution of Xen in Debian is that it depends on the external world for a few things, like bootstrapping a new VM. I haven't used anything that stacks on top of Xen or the scripts provided by Debian, though and I suspect that there is a healthy management system for it somewhere on the Internet. I would like to play more with getting Xen to be automatically controlled in a setup not unlike Linode's setup, someday, with the ability to do automatic provisioning and system setup, as well as things like live migration. </p>
<p>I am curious as to how KVM is more flexible than Xen, though. The overhead is far greater since it is actually emulating hardware, and the only interface to KVM that I am aware of is the KVM fork of QEMU, which is essentially just QEMU, as I understand it, with the KVM system being used to accelerate the CPU emulation. Or is there now a command line interface that allows things to be more efficient yet and drop things like the VGA chipset and other hardware emulation? </p>
<p>Anyway, just wanted to really mention the face that the upstream/mainline kernel supports execution on Xen natively now. :-) I think that happened extremely late in the 2.6 series, maybe 2.6.38 or 2.6.39, IIRC. </p>
<p>--<br>
Sent from my Android device. Sorry for any typos,<br>
autocorrect is sometimes a pain in the rear.</p>
<div class="gmail_quote">On Jul 13, 2012 12:23 PM, "JD" <<a href="mailto:jdp@algoloma.com">jdp@algoloma.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On 07/13/2012 10:40 AM, Chuck Payne wrote:<br>
> Guys,<br>
><br>
> Anyone using Citirix Xen? I just started a new job and they are using<br>
> it as their Virtual Server, but I am seeing a lot of issues, before I<br>
> go and recommend a change, I like to hear some feed back, but Pro and<br>
> Con. I am a bit basis as I have use VMWare ESXi and KVM.<br>
><br>
> Just so note some of the issues we had so far, lots of kernel panics<br>
> with NFS. Virtual Machines being rebuild because of issues with the vm<br>
> themselves, such as drives going bad. Not being able to reboot<br>
><br>
<br>
I've been using paravirtual Xen since mid-2008, not the Citrix specific version.<br>
To get more flexibility, we're migrating to KVM. We've migrated off ESXi, Xen,<br>
and VirtualBox VMs so far. These are servers. For desktop virtualization, both<br>
VirtualBox and KVM are used still. There are still 5 Xen DomUs to be migrated.<br>
<br>
Our use of Xen was pretty simple. Only Linux clients running the same distro and<br>
no HVM. I tried to get a Windows VM running using HVM, but didn't have the<br>
luxury of lots of downtime on those hosts, so when it didn't immediately work<br>
with a few hours of effort, we stopped trying. Windows DomUs run well enough<br>
under KVM. I've have a Windows7 Media Center recoding TV with dual network<br>
tuners that way for about 9 months. HDD performance is a different issue with<br>
Windows DomUs, however.<br>
<br>
Xen was pretty solid, but when the hostOS had a kernel patch, I found it was<br>
about 15% likely that it wouldn't boot up with the new kernel. It isn't fun to<br>
see a kernel panic at that point, usually around 4am on a Saturday morning. I'd<br>
have to drop back to a previous kernel for about a week as other modules were<br>
released to handle the newer kernel. This issue happened about once a year. Once<br>
Xen was up and running, it stayed up. Never crashed unless there was a hardware<br>
error. Hardware failures will take any hyper-visor down.<br>
<br>
I think we run Xen v3.2 .... each version has different capabilities and<br>
compatibilities. I'm certain we could run a newer version of Xen, if we wanted<br>
to manage kernels.<br>
<br>
I manually created each Xen VM config file and learned a few lessons about<br>
forcing MAC addresses to the client OSes so network monitoring was useful at<br>
all. Without that, new, random MACs were created at every DomU boot.<br>
<br>
Also we only used the CLI interface (xm) to manage each VM. It appears to me<br>
that the virsh CLI interface provides similar capabilities, so the that part of<br>
the learning curve isn't steep at all. I'm pretty certain that newer libvirt<br>
and virt-manager handle recently created Xen VMs now - at least for the last<br>
year or so. It doesn't work with our old Xen Dom0, however.<br>
<br>
If they are big into Xen and happy with it, I don't know that I'd change, unless<br>
they are unhappy with the support or license costs. It also matters which<br>
clientOS is being run the most. For mostly Linux VMs, then KVM is a good<br>
choice, but if mostly Windows DomUs, the choice becomes more difficult.<br>
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