[BBLISA] ntp question

[Rudie, Tony]

ntpd isn't perfect at dealing with VMs either.  My organization has a cron job to monitor ntpd and make sure the time is still accurate, and there's some sophisticated logic there to minimize false positives, but it still throws a couple of valid alerts every week, (always on VMs.  The job runs everywhere, but...) and restart ntpd.  

Actually, it's not a cron job.  The monitoring system runs the check-script, and throws the alert based on return code.  


 - Tony Rudié 

-----Original Message-----
From: bblisa-bounces at bblisa.org [mailto:bblisa-bounces at bblisa.org] On Behalf Of Dewey Sasser
Sent: Tuesday, March 17, 2009 5:08 PM
To: Edward Ned Harvey
Cc: L-bblisa
Subject: Re: [BBLISA] ntp question

Edward Ned Harvey wrote:
> Instead, I use cron to schedule ntpdate once per hour on every machine.  It
> may be less precise (because the clock is allowed to drift, and only gets
> corrected once per hour) but it's a whole lot more reliable.  How far off
> does the clock drift over the course of an hour?  Typically, I'd say a
> second.  Maybe five seconds if you're really pushing it.  I don't care about
> that for any purposes in my infrastructure.  I care about the reliability
> more.
>   
(Note:  I'm the de facto admin for the network Eric is talking about.)

That's a good point, and I've actually tried that methodology on a host
of systems.  One problem I've encountered is that many of our "systems"
are actually VMWare based virtual machines and VMWare seems to have a
borderline ridiculously bad clock drift.  From what I've read on the
'net (which, as we all know, is always true) this can somehow manifest
as either lead as well as lag.

I have observed some of our virtual machines which were synchronized
hourly with ntpdate to drift several minutes apart over the course of
their hour.  This seems to have made e.g. NFS very unhappy.

--
Dewey

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