[ale] Citrix Xen

[JD]

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.