[ntp:questions] Re: Correcting my time servers clock drift on Alpha ES40s / Tru64

CBee I.Dont at want.your.spam
Wed Nov 9 08:56:10 UTC 2005


brett.sander at tenix.com wrote:

> Hi,
> 
> We have 2 ES40 Alpha servers running Tru64 Unix and they are configured
> as peers using their local clocks.  We configred them this way for
> redundacny, so that if one died the network would still have a time
> server.

Having 2 clocks is the worst setup you can have. With 1 clock, there is just 1 
time which must be perfect. With 2 clocks, there are 2 times both equal in their 
quality. If they differ, it is impossible to find the best time. With 3 or more 
clocks an optimal time can be calculated from the relative offset between them. 
Like 2 are equal, 1 differs: the one that differs is wrong, the other is good. 
If all three differ, there is some math to find the relative best time.

With more than 3 this calculation can get even better. NTP can be configured 
with loads of clocks, it will only use about 3 to 5 at any time, it will 
constantly test the relative quality and change if needed.

Our setup is as follows:
our timeserver uses the clock provided by our internet provider (well, all three 
references are defined).
Other servers are grouped in their usage. within a group (like all domain 
controllers) they use each-other as peer and the one timeserver as server.


> 
> The ntp.conf files are configured as such:
> 
> terrance's ntp.conf:
> 
> peer phillip
> peer 127.127.1.1

Most current linux distro's setup the local clock as follows:

server  127.127.1.0     # local clock
fudge   127.127.1.0 stratum 10

This way it is only used as last resort: as long as there is an other reference, 
that one is used.

> 
> phillip's ntp.conf:
> 
> peer terrance
> peer 127.127.1.1
> 
> Currently they have been up and running for about 14 months and the
> clocks are now about 30 minutes slow.

I recon they have both the same offset. This is mainly due to the relative 
quality you give to the build-in clock. Better not do that (see above)

> 
> Any ideas how I can better configure these 2 servers to keep the clocks
> no time.  Also, whats the best method to update the time (I was just
> going to use date to set the time)
> 
> Another thing is these servers have no access to the internet at all.


You somehow need an external reference clock. Either any other machine or an 
external reference clock. Otherwise, an offset must be accepted and/or manually 
corrected.



CBee




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