I posted this before in the XEN NG, but I got no suitable answer.
"What is the better solution?
1) use ntp in the XEN host and synchronize the guests with the clock
running on the control domain (independent_wallclock=0, what the
2) or use ntp in host and guest (and independent_wallclock=1)
I ask, because the XEN host (bare metal) has a more stable clock and
if the ntp servers are fail, the guest VMs can all rely on host clock,
all should guest VMs then are running in sync.
But I heard some bad things about the synchronization with the host
clock, users in internet recommend to use ntp in guest VM. My mind
tells me, to use ntp (2), but my brain in stomach is telling me, to
use syncing via XEN method (1).
The only answer in the NG was:
"PV ops (AKA upstream) Linux kernels only support option (2), so that is
what you need to use for them.
Only the classic Linux kernel port (not upstream) supported
independent_wallclock=0, I don't know if other PV OSes (e.g. *BSD)
supported this option or not. I'm pretty certain no OS running in HVM
(including Linux as HVM or PVHVM) supported dependent wallclock."
But what kind of kernel is delivered with SLES?
Does the Kernel support wallclock or not, is it a "upstream" or a classic.
I presume, that is a upstream, but then, no wallclock is supported.
In this case the clock is only synchronized to the RTC, if no NTP is configured?
myserver:~ # rpm -qi kernel-xen
Name : kernel-xen Relocations: (not relocatable)
Version : 3.0.74 Vendor: SUSE LINUX Products GmbH, Nuernberg, Germany
Release : 0.6.10.1 Build Date: Sat May 25 12:24:18 2013
Install Date: Thu Jul 11 11:42:20 2013 Build Host: furud
Group : System/Kernel Source RPM: kernel-xen-3.0.74-0.6.10.1.nosrc.rpm
Size : 81262704 License: GPL v2 only
Signature : RSA/8, Sat May 25 12:29:05 2013, Key ID e3a5c360307e3d54
Packager : http://bugs.opensuse.org
URL : http://www.kernel.org/
Summary : The Xen Kernel
The Linux kernel for Xen paravirtualization.
This kernel can be used both as the domain0 ("xen0") and as an unprivileged
("xenU") kernel when 64-bit; on 32-bit it can only be used in unprivileged