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 bill@scconsult.com