[ale] Citrix Xen

[Michael Trausch]

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.

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.

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?

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.

--
Sent from my Android device. Sorry for any typos,
autocorrect is sometimes a pain in the rear.
On Jul 13, 2012 12:23 PM, "JD" <jdp at algoloma.com> wrote:

> On 07/13/2012 10:40 AM, Chuck Payne wrote:
> > Guys,
> >
> > Anyone using Citirix Xen? I just started a new job and they are using
> > it as their Virtual Server, but I am seeing a lot of issues, before I
> > go and recommend a change, I like to hear some feed back, but Pro and
> > Con. I am a bit basis as I have use VMWare ESXi and KVM.
> >
> > Just so note some of the issues we had so far, lots of kernel panics
> > with NFS. Virtual Machines being rebuild because of issues with the vm
> > themselves, such as drives going bad.  Not being able to reboot
> >
>
> I've been using paravirtual Xen since mid-2008, not the Citrix specific
> version.
> To get more flexibility, we're migrating to KVM.  We've migrated off ESXi,
> Xen,
> and VirtualBox VMs so far. These are servers. For desktop virtualization,
> both
> VirtualBox and KVM are used still.  There are still 5 Xen DomUs to be
> migrated.
>
> Our use of Xen was pretty simple. Only Linux clients running the same
> distro and
> no HVM. I tried to get a Windows VM running using HVM, but didn't have the
> luxury of lots of downtime on those hosts, so when it didn't immediately
> work
> with a few hours of effort, we stopped trying.  Windows DomUs run well
> enough
> under KVM. I've have a Windows7 Media Center recoding TV with dual network
> tuners that way for about 9 months. HDD performance is a different issue
> with
> Windows DomUs, however.
>
> Xen was pretty solid, but when the hostOS had a kernel patch, I found it
> was
> about 15% likely that it wouldn't boot up with the new kernel. It isn't
> fun to
> see a kernel panic at that point, usually around 4am on a Saturday
> morning.  I'd
> have to drop back to a previous kernel for about a week as other modules
> were
> released to handle the newer kernel. This issue happened about once a
> year. Once
> Xen was up and running, it stayed up. Never crashed unless there was a
> hardware
> error.  Hardware failures will take any hyper-visor down.
>
> I think we run Xen v3.2 .... each version has different capabilities and
> compatibilities. I'm certain we could run a newer version of Xen, if we
> wanted
> to manage kernels.
>
> I manually created each Xen VM config file and learned a few lessons about
> forcing MAC addresses to the client OSes so network monitoring was useful
> at
> all. Without that, new, random MACs were created at every DomU boot.
>
> Also we only used the CLI interface (xm) to manage each VM.  It appears to
> me
> that the virsh CLI interface provides similar capabilities, so the that
> part of
> the learning curve isn't steep at all.  I'm pretty certain that newer
> libvirt
> and virt-manager handle recently created Xen VMs now - at least for the
> last
> year or so. It doesn't work with our old Xen Dom0, however.
>
> If they are big into Xen and happy with it, I don't know that I'd change,
> unless
> they are unhappy with the support or license costs. It also matters which
> clientOS is being run the most.  For mostly Linux VMs, then KVM is a good
> choice, but if mostly Windows DomUs, the choice becomes more difficult.
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