[time-nuts] Tracking NTP displacement and correlation betweentwo clients.

bownes bownes at gmail.com
Fri Oct 5 22:57:03 UTC 2012


Comments inline. 

On Oct 5, 2012, at 18:26, Hal Murray <hmurray at megapathdsl.net> wrote:

> 
> bownes at gmail.com said:
>> The problem is that they start in sync and over the course of a day drift
>> that far apart despite having NTP running. We're not sure why NTP isn't
>> correcting it along the way. Though at this point, we are looking at a
>> firmware bug.
> 
> I wouldn't think of it as two systems drifting apart, but rather at least one 
> system with a broken clock.
> 

Correct. 

> Is it only one system that is broken?
> 

Sort of. There are several systems consisting of a matched pair of nodes. In each case, one of the two wanders out into the weeds. But not every pair has one that goes south. 

In this case, four systems, 8 nodes, all identical hw (sequential sn's even), identical iLOM/DRAC, same software the entire length of the stack. 

Installing the latest firmware patch appears to have solved the problem. I'll know next week. 


> How many systems do you have running the same firmware?

<redacted>

> Normally, if ntpd is off by more than 128 ms, it will step the clock.  That 
> puts a line in the log file.  So it's more than a bit strange that the clocks 
> get off by many seconds.
> 

My thinking exactly. But it wasn't. I was hoping to use some tools to watch it drift off. 

> I'd double check that ntpd really is still running.

It is. 

> Are your drift-apart systems using only your 2 local stratum-2 servers?  If 
> so, that may be the problem.  If those servers don't agree, which one do you 
> believe?  (There is endless discussion in the NTP community about how many 
> servers you need.  3 lets you out-vote 1 bad guy.  4 lets you out-vote a bad 
> guy if one of them is down. ...)
> 

Two NTP servers agree. They even agree with my S1 at home. :)

Thanks for all the help folks. It looks like it was a firmware bug, even if I can't explain how the firmware was causing the NTP clock to be off. 




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