Posted by Unruh on 07/02/07 01:15

ibuprofin@painkiller.example.tld (Moe Trin) writes:

>On Sat, 30 Jun 2007, in the Usenet newsgroup comp.os.linux, in article
><dZxhi.4257$Io4.646@edtnps89>, Unruh wrote:

>>ibuprofin@painkiller.example.tld (Moe Trin) writes:

>>>I'd change network providers too. In the thirty-four years I've been
>>>in networking, the longest we've been disconnected is six hours - the
>>>classic 'backhoe fade' thanks to the city water department.

>>Look, if you are really that desperate for accurate times, get a gps
>>receiver with pps capability.

>I'm not desperate for accurate times - we've been setting our servers
>to a time standard for decades. We started by using the time ticks from
>WWVB back in the 1970s, before we had IP. We've had GPS time receivers
>for at least seven years, but that's in addition to the use of NTP pool
>servers and company peers (which - surprise, surprise - also have GPS
>receivers and use NTP pool servers).

>>That will keep your system accurate to microseconds . And it will not
>>go off when your network disconnects.

>Actually, that wake-up call from the city occurred back in ~1992, and
>prompted us to get redundant network connections in the same year. The
>fun is verifying that your connections are indeed redundant, and not
>running in the same conduit as leased pairs from your primary provider.

>>And they are cheap ( the one I bought was less than $100) Use ntp to
>>sync to it, not to th enetwork ( which is certainly not good to even
>>msec, never mind microseconds).

>Maybe you want to read the NTP documentation. If all you have is one
>time source, you are indeed unable to correct for propagation delays.
>But if you have more than that (can you say "redundancy" Bill? I
>though you could), you can deduce and eliminate nearly all of the
>delays.

What delays? The delay between the gps receiver and the computer it is
attached to is a usec at most.

However redundancy is good, esp is someone decides to disconnect your gps.

I guess you meant that you have one gps receiver which acts as a stratum
one to a whole bunch of other systems. Then yes, redundancy can be useful.
On the other hand just put one on each critical machine and be done with
it.



>>Then slave your other computers to that one as a stratum 1 server.

>-rw-rw-r-- 1 gferg ldp 43295 Nov 18 2005 TimePrecision-HOWTO

>>> Thus, there are three time servers here, each monitoring _separate_
>>> time sources, and averaging that to 'tweak' their own concept of
>>> correct time, and we're not even subject to those regulations - they
>>> are only serving time to 2500+ users in this facility, and acting as
>>> a stratum 4 reference to other time servers in other company locations.
>>
>>Why not get a gps clock with the network as backup?

>Read the docs from Dave Mills at UofDelaware. He writes pretty well.

Yes, have done so. Just which point was it you wanted me to read?



> Old guy

[Back to original message]