[Dovecot] VMware and Time moved backwards

[Peter Hessler]

never ever ever run ntp on virtual hardware.

instead, run ntp on the host hardware, and tell the client to always 
obey the bios clock.  I add "* * * * * /sbin/hwclock --localtime --hctosys"
to my crontab for that.



On 2008 May 21 (Wed) at 20:27:09 +0200 (+0200), 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
:
: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? 
:
:According to Timo's postings, workarounds within the dovecot itself to
:cope with "time moved backward" problems are not planned yet to be
:impelented.
:
:So best regards,
:Robert
:
:

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