[time-nuts] Noob question, NTP stratum 1.

[Achim Gratz]

wildylion via time-nuts writes:
> Situation 1:
> What I currently have is a uBlox M8N GPS puck I'm planning to use with
> the Raspberry PI. Seems like it should work almost out of the box with
> some kernel tuning, but I have a question about short term stability
> in the event of GPS loss - how well will the board hold over if it's
> lost GPS for, say, 24 hours?

You can't say, really.  It all depends on how the GPS gets lost, or what
the environment does around the time of loss and after.  If you have
multiple such NTP servers you'll quickly learn by comparing them to each
other that they sometimes do things you didn't think they should be
doing.  If you have just one, you'll probably never even know that.

> Situation 2:
> Also, there's a need for more dependable NTP time sources for our colocated spaces.

Colocated spaces == racks where paying customers put their stuff?

> What we have is about 100 servers, some of them running DBMS that
> wouldn't like clock drift at all. After a recent incident involving
> NTP I've got an idea to install GPSDO time servers in each datacenter
> and slave them to stratum2's that will be actually distributing time
> to clients.

You should really think about doing PTP instead on these systems,
preferrably over a dedicated network.

> All the certified GNSS disciplined clocks are really expensive (way
> more than the management would approve), so what I'm planning to do is
> possibly getting a couple LeoNTP units and using them as the root time
> sources, would this be a good plan?

Nothing against the LeoNTP (which I'm unfamiliar with), but if time
actually is important (i.e. you need to guarantee some level of
performance rather than hope for it) you'll end up doing the majority
of the work that you'd otherwise buy with the certification.  That
almost certainly ends up being more costly than getting the certified
gear.

> Of course, all the NTP infrastructure will be monitored, and possibly
> we'll use Stratum 2 servers which would be slaved to GPSDO S1's AND
> the public NTP pool for sanity checks.
>
> Maybe BG7TBL's units instead of LeoNTP?
> Is that a good idea?

That really depends on what you are trying to achieve, but I'd say you
have yet to define what the problem is that you're trying to solve.  Do
you just want your 100 servers to have the same time within some defined
boundary, does that time need to track the official/legal time (at what
maximum offset) or do you need to have traceable time stamps all the way
back to the source (at what resolution and error)?  For each set of
answers entirely different architectures would be appropriate.


Regards,
Achim.
-- 
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