What about Xen? (RE: NTP problem for virtual RHEL 4 server on VmWare)

[George Magklaras]

We have various paravirtualized (RHEL5 on RHEL5) domains, running MySQL 
RDBMSes and a number of other tools for which time synchronization is 
critical. What we tend to do is to point (via bridged interfaces) to the 
host OS (Dom 0) and then the guests are NTP clients.

However, all the money is on how you start and stop/suspend your guest 
OSes. When we start up the array of guests, we make sure that the guest 
domains are up, that NTP has started and that time is synced. The way we 
do this is by taking various epoch time stamps (see perl localime 
function) and look for deviation (simple perl script) by means of yet 
another time synced bespoke guest. This can be performed effectively if 
you setup a non-privileged ssh key enabled account. As long as the guest 
connects to ntpd, it proceeds to perform the check on the rest of the 
clients. If that completes successfully, it marshals the start the 
mounting of NFS dirs and the start of the RDBMS engines  and the rest of 
the stuff. In addition, we do not allow users of the guest systems to 
shutdown/or suspend them arbitrarily and/or change the scheduling 
priority of each domain.

The same check is performed when we are about to shutdown the domains, 
all RDBMSes shutdown, NFS systems unmounted and lights off.

This model has worked so far and we have not seen any NTP hickups. To 
start an array of say 100 guests, it takes approximately 10-15 minutes 
from the point you press click (or the point that all of them start the 
domains, all the way to user login and RDBMS access). So, it's not fast, 
but it works.

GM

-- 
--
George Magklaras

Senior Computer Systems Engineer/UNIX Systems Administrator
EMBnet Technical Management Board
The Biotechnology Centre of Oslo,
University of Oslo
http://folk.uio.no/georgios




Miner, Jonathan W (US SSA) wrote:
> Changing the subject slightly....
> 
> What are peoples' experiences with Xen?  I typically run NTP on the physical (host) operating system, and run no time synchronization on the guest operating systems.  I don't have any problems... or at least I don't think I have any.
> 
> - Jon
>