At 8:27 PM +0200 5/21/08, Robert Henjes wrote:
Hi,
I followed the discussions regarding the "time moved backward" problem
and the use of ntp in such cases. At our department we are running two
dovecot servers within an vmware server environment, and unfortunately
the timedrift (with ntpd active) exceeds sometimes up to 30 minutes
virtual drift within 10 minutes realtime (mostly into future). This is
due to some overcorrections within the TSC algorithms of the vmware
virtual machine.
More information and some hints to workaround are documented here:
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1420
That page seems to say that running ntpd inside a VMware guest is not
a good choice. I would think that you'd be best off doing what your
vendor advises on that page, at least as a start, rather than
trusting in the consistently brilliant and consistently unified
consensus view of the Dovecot admin community on a question which is
only very tangentially related to Dovecot.
Nevertheless we are currently working on evaluating a stable solution by
doing some system measurements, which would be the best option to cope
with this problem, since the XEN environment seems to have a similar
issue.
Running "ntpdate -u" as a cronjob is not an option due to two facts:
a) Time is moving quickly and may cause "major problems" ;)
b) It is not recommended by the vmware team itself as well
We are currently considering two options:
a) Using the "clock=pit" kernel option, which may cause the system to be
to slow
b) using vmware tools and use only the ntp synchronisation of the host
(we have currently only little experience with this). Also vmware tools
are somewhat critical in case of updates. So our intention was to
use as less vmware specific things as possible within the virtual
machine, so only our host itself depends on vmware specific software.
The question is, which option would you prefer? Is there another
solution beside the mentioned ones?
I think that trying to avoid VMware-specific software in a VMware
environment is unwise. VMware software is what provides your virtual
system with a clock.
--
Bill Cole
[EMAIL PROTECTED]
