[H-GEN] TimeZones and Redhat 8.0

[Greg Black]

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ben.carlyle at invensys.com wrote:

| > ... unless there is a
| > high-speed and low-latency connection to a stratum 1 or stratum
| > 2 server, the synchronisation to the real time will be lucky to
| > average better than 20 to 50 milliseconds.  Of course, this is
| > good enough for lots of purposes, but it's much less good than
| > the NTP people would have you believe.
| 
| Of course, the NTP people recommend that you have at least three 
| seperately sourced time servers available to your network to get any kind 
| of reliability ;)

As I recall (it's years since I last read the documentation in
any detail), they don't make this point particularly clearly.
And, it's a bit of a moot point -- if you have the connectivity
to meet that requirement, you probably have local reference
clocks anyway; and if you're small enough not to have the local
reference clocks, you'll never have good enough separate pipes
to reference clocks (assuming you even have separate pipes) to
overcome the problems.

And, from personal experience when accessing reference servers
over ADSL lines and the like, the more stratum 2 servers you use
over the same wire, the more chaotic your timekeeping seems to
get.  It's a non-trivial problem to solve.

| NTP could be a better product than it is, but I think that it's not the 
| kind of work that most people want to get into :) They say that once you 
| know sendmail you'll never escape your destiny of supporting it, and 
| perhaps NTP has a similar strange attractor effect.

That certainly is the impression I have formed.  I know for
certain that I don't ever want to get into NTP programming.

| That said, it's 
| probably still the best thing out there for arbitrary LAN/WAN 
| time-synchronisation configurations available.

Agreed.  It's just useful for people to know that it's far from
a perfect solution and that it needs care and feeding much more
regularly than most of the daemons that you might be inclined to
run.

Greg

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