[ntp:questions] Re: uk pool problem
ecoca at eed.usv.ro
Fri Sep 1 20:04:18 UTC 2006
Chris Davies wrote:
> Eugen COCA <ecoca at eed.usv.ro> wrote:
> > 1. Use ntpd not ntpdate;
> > 2. Use a large number of servers (more than 9);
> That seems rather excessive. If you're using the Pool at all, then three
> or so should be enough. (If you want better time keeping, use specific
> servers rather than the Pool.)
It doesn't matter if a server is or not in the pool. From the point the
view of NTP more servers, theoreticaly, means more accuracy. I said
theoreticaly because I had a very bad experience with one of my server.
I have the GPS and the PPS souces and a number of "reference" servers
in order to sync to a source if the GPS is not available. Due to
extreme network condition (the packets where routed on different routes
when going from and respectivelly when comming to my server), all ntp
servers where 40 ms of the real time. So, ntpd dropped the GPS source
as bad and synced with the external servers. The problem was solved by
using the "noselect" option for all external servers.
> > 3. Use pool servers and manually entered servers addresses;
> As I understand it, the point of the Pool was to offer an easy way for
> people to configure their clients, without needing to find addresses of
> specific servers. If you've got explicit servers configured, then you're
> unlikely to need the Pool as well.
I do not agree with this opinion. I'll explain why: the pool contains
very many servers. Some of them are "premium" server, others are
"second-hand" servers and the worst category is "sporadic servers".
"Premium servers" means that the server is at least GPS synced or,
better, GPS + PPS (minimum from the GPS or better with OCXO, Rb, CS or
H). These are dedicated servers with UPSs and very good network
connection (min. 10Mbps to Internet up/down, not x/ADSL links !). And,
very important, an administrator to log-in every day or to look to the
logs ... In this category you may find no more than 20 percent from the
total. I have 3 servers in this category at my location. "Second-hand"
servers are usually Stratum 2 servers, synced on Internet with Stratum
1 servers. Many Stratum 2 servers in the pool are not only time
servers, they are web, mail, ssh, etc (try to connect to specific port
and you'll find out I'm right) servers. I' estimated to 60 percent the
number of these servers. "Sporadic servers" are the servers that are
not switched-on all the time or are Stratum 3 or more. The pool have a
good time reference server to compare with the time received from the
servers in the pool and making a score.
In conclusion, it is always better to use some "premium" servers in
your conf file.
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