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

[Bob kb8tq]

Hi

One of the gotcha’s with “cell phone” based timing is discovering that the 
provider
has been a bit lax about making sure the time stamp on the signal is what it 
should 
be. The problem is less common with 800 MHz CDMA than other bands / services. 
One of the reasons we see a lot of this sort of gear on the secondary market is 
that
… errr …. they had problems ….  ( = trust but verify ….)

Bob

> On Jul 22, 2019, at 7:38 PM, K5ROE Mike  wrote:
> 
> You may want to look at something an Endrun CDMA ntpserver for the 
> datacenter; don't need view of the sky. Available on the used market sub $1k
> 
> Standard solution for this scenario.
> 
> 
> K5ROE Mike
> 
> On 7/22/19 10:50 AM, wildylion via time-nuts wrote:
>> Yeah, of course I will NOT do anything home-grown for the datacenter.
>> 
>> But currently it uses 3 Stratum 2 NTP servers, one per DC, with them 
>> referencing a list of 4 close-by Stratum 1 sources.
>> 
>> ntpstat generally says that time is correct within ~50 ms, while jitter and 
>> offset generally don't exceed 1ms, the root dispersion is quite large.
>> Also these Stratum 2 NTPs are run from Cisco routers, which I doubt are very 
>> good at timekeeping.
>> 
>> When I implemented this scheme, I offered to have S2 on a set of x86 
>> servers, but was overruled by management who said it'll be better if we run 
>> S2's off Cisco gear.
>> 
>> So what if we add a couple GPSDO's into the mix, using them as primary time 
>> sources alongside public Stratum1 NTP servers for sanity check? And of 
>> course moving the S2's to something more stable.
>> 
>> My own, homegrown S1 pool NTP is another matter entirely - I think just a 
>> tuned Raspi with a M8N will be enough?
>> 
>> Sent with [ProtonMail](https://protonmail.com) Secure Email.
>> 
>> ‐‐‐ Original Message ‐‐‐
>> On Monday, 22 July 2019 г., 17:38, Taka Kamiya  wrote:
>> 
>>> If you have 100 production servers with database, I am going to strongly 
>>> discourage you from taking a "home grown" route.  You will need multiple 
>>> redundant implementation with fail-over.  You mentioned budget.  How much 
>>> are your bosses willing to pay for consultation fees for failed or 
>>> corrupted data?  I am assuming you are talking about Oracle RDBMS with 
>>> minimum of 2 way RAC.
>>> 
>>> If you are using collocation services, doesn't the center itself offer ntp 
>>> service for fee?
>>> 
>>> If you need 24 hour hold-over, I will take nothing less than multiple 
>>> ovenized crystal OSC GPSDO with redundancy per center.  Then feed that into 
>>> ntp server with multi-location fail over.
>>> 
>>> If I were responsible for managing such system and if my boss will want me 
>>> to go cheap route, I will seriously fight it.  If it's successful, your 
>>> boss will get credit for spending little and getting a big benefit.  WHEN 
>>> it fails, it's going to be your fault for not mitigating risk sufficiently. 
>>>  Try pricing out 2 days of consulting fees
>>> 
>>> ---
>>> (Mr.) Taka Kamiya
>>> KB4EMF / ex JF2DKG
>>> 
>>> On Monday, July 22, 2019, 10:05:56 AM EDT, wildylion via time-nuts 
>>>  wrote:
>>> 
>>> Hello there,
>>> 
>>> I wanted to ask for advice regarding NTP
>>> 
>>> 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?
>>> 
>>> Situation 2:
>>> Also, there's a need for more dependable NTP time sources for our colocated 
>>> spaces.
>>> 
>>> 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.
>>> 
>>> 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? 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?
>>> 
>>> Sent with [ProtonMail](https://protonmail.com) Secure Email.
>>> ___
>>> time-nuts mailing list -- time-nuts@lists.febo.com
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>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>> and follow the instructions there.
>> ___
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>> 

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

[Achim Gratz]

Achim Gratz writes:
> The thing to note is that you need to boot with "nohz=off",

Tom was asking what that kernel parameter meant and does.

UNIX used to have a fixed frequency interrupt called TICK that would do
its thing HZ times per second (typically HZ=100, but later on HZ=1000 on
some systems).  Without going to deep into the details, many powqer
saving features don't really work if you wake up the CPU too often, so
something called a "tickless" Linux kernel was developed and the config
switch to use it is CONFIG_NO_HZ.  The tick interrupt is still there in
such a kernel, but it can be suppressed in order to save power.  The
kernel poarameter "nohz=off" tells the kernel to not use this facility
and hence faithfully run a kernel interrupt for each TICK.  It also
prevents the kernel from shifting the deadlines of other kernel timers
in order to create "bunches" of work, which is what I needed in this
case.

Just one reference, you can dive in from there if you need to know more:
https://stackoverflow.com/questions/9775042/how-nohz-on-affects-do-timer-in-linux-kernel


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf Blofeld V1.15B11:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada

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

[Achim Gratz]

wildylion via time-nuts writes:
> The point is: do we ever need S1 NTPs? I think, this could be a nice
> addition if properly realized, but right now I'm not sure if I can
> propose it.

You really can't properly monitor any stratum-2 sources you have
configured if you don't have your own stratum-1 and you need at least
three independent ones to rule out any irregularities in them with high
enough probability.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Waldorf MIDI Implementation & additional documentation:
http://Synth.Stromeko.net/Downloads.html#WaldorfDocs

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

[Steven Sommars]

US operators are planning to shut down their CDMA networks.  See for example
https://www.fiercewireless.com/wireless/verizon-to-shut-down-2g-cdma-1x-network-by-end-2019

I wouldn't be surprised to see this date get pushed back though.



On Mon, Jul 22, 2019 at 8:05 PM K5ROE Mike  wrote:

> You may want to look at something an Endrun CDMA ntpserver for the
> datacenter; don't need view of the sky. Available on the used market sub
> $1k
>
> Standard solution for this scenario.
>
>
> K5ROE Mike
>
> On 7/22/19 10:50 AM, wildylion via time-nuts wrote:
> > Yeah, of course I will NOT do anything home-grown for the datacenter.
> >
> > But currently it uses 3 Stratum 2 NTP servers, one per DC, with them
> referencing a list of 4 close-by Stratum 1 sources.
> >
> > ntpstat generally says that time is correct within ~50 ms, while jitter
> and offset generally don't exceed 1ms, the root dispersion is quite large.
> > Also these Stratum 2 NTPs are run from Cisco routers, which I doubt are
> very good at timekeeping.
> >
> > When I implemented this scheme, I offered to have S2 on a set of x86
> servers, but was overruled by management who said it'll be better if we run
> S2's off Cisco gear.
> >
> > So what if we add a couple GPSDO's into the mix, using them as primary
> time sources alongside public Stratum1 NTP servers for sanity check? And of
> course moving the S2's to something more stable.
> >
> > My own, homegrown S1 pool NTP is another matter entirely - I think just
> a tuned Raspi with a M8N will be enough?
> >
> > Sent with [ProtonMail](https://protonmail.com) Secure Email.
> >
> > ‐‐‐ Original Message ‐‐‐
> > On Monday, 22 July 2019 г., 17:38, Taka Kamiya 
> wrote:
> >
> >> If you have 100 production servers with database, I am going to
> strongly discourage you from taking a "home grown" route.  You will need
> multiple redundant implementation with fail-over.  You mentioned budget.
> How much are your bosses willing to pay for consultation fees for failed or
> corrupted data?  I am assuming you are talking about Oracle RDBMS with
> minimum of 2 way RAC.
> >>
> >> If you are using collocation services, doesn't the center itself offer
> ntp service for fee?
> >>
> >> If you need 24 hour hold-over, I will take nothing less than multiple
> ovenized crystal OSC GPSDO with redundancy per center.  Then feed that into
> ntp server with multi-location fail over.
> >>
> >> If I were responsible for managing such system and if my boss will want
> me to go cheap route, I will seriously fight it.  If it's successful, your
> boss will get credit for spending little and getting a big benefit.  WHEN
> it fails, it's going to be your fault for not mitigating risk
> sufficiently.  Try pricing out 2 days of consulting fees
> >>
> >> ---
> >> (Mr.) Taka Kamiya
> >> KB4EMF / ex JF2DKG
> >>
> >> On Monday, July 22, 2019, 10:05:56 AM EDT, wildylion via time-nuts <
> time-nuts@lists.febo.com> wrote:
> >>
> >> Hello there,
> >>
> >> I wanted to ask for advice regarding NTP
> >>
> >> 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?
> >>
> >> Situation 2:
> >> Also, there's a need for more dependable NTP time sources for our
> colocated spaces.
> >>
> >> 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.
> >>
> >> 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? 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?
> >>
> >> Sent with [ProtonMail](https://protonmail.com) Secure Email.
> >> ___
> >> time-nuts mailing list -- time-nuts@lists.febo.com
> >> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> >> and follow the instructions there.
> > ___
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> > To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
>
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> To 

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

[Peter Membrey]

Hi guys,

A little late to the party but hopefully someone finds this useful.

As the Raspberry Pi family of IoT devices are so popular and have been used in 
a host of different research projects to gather data (much of it including 
timing information), we were curious as to how stable the Raspberry Pi was and 
whether it was suitable for such work. To understand this better we 
characterised the main counter on the board (the STC) for all three generations 
of Pi available at the time. We presented the results at IMC2016 in "Time to 
measure the Pi" which is available here:

http://crin.eng.uts.edu.au/~darryl/Publications/Pi-hat_current.pdf

We also looked at how well it performed with NTP and also characterised the 
uBlox M8Q as a potential time source.

The Pi's (especially the latest generation at the time, the Pi 3) did 
surprisingly well and behaved similarly to what we previously observed in a 
"big box" machine.

In terms of its suitability as an NTP server, again it held up really well. 
That said until the Pi 4 (which I am still waiting to get my hands on), the 
network interface on the Pi goes through an internal USB hub and suffers from 
significant jitter. I've not sat down and studied it in depth, but initial 
tests showed occasional spikes well into the millisecond range.

Lastly although the Pi's are impressive given their price point and they can 
perform well for many use cases, there is a reason why Microsemi sells their 
solutions for 100x the price. At home or in the office, a Pi3 with a uBlox M8Q 
(with a good view of the sky) is likely to give you better results than using a 
random server from the Internet's NTP Pool, but I wouldn't want to bet on it 
for keeping critical infrastructure in sync (it's not going to do well in 
holdover situations for example).

Kind Regards,

Peter Membrey



- Original Message -
From: "Luiz Paulo Damaceno" 
To: "wildylion" , "Discussion of precise time and 
frequency measurement" 
Sent: Tuesday, 23 July, 2019 01:31:34
Subject: Re: [time-nuts] Noob question, NTP stratum 1.

Dear colleagues, i've made some tests and wrote an article about Raspberry
Pi as a timeserver. I think we can trust on it and this board can keep a
good time from GNSS PPS. I'm open to suggestions. I hope this can help in
the decision making process. The link: rpi_article
<https://www.researchgate.net/publication/334179026_Credit_card_size_computer_Stratum_1_NTP_Server>

Also, in our tests as you can see in the article, for general purposes the
RPI has a good dealing with high loads. The difference is we've removed the
crystal oscillator and put a signal from a synthesizer, you can keep the
crystal and trust on pps signal too. I'm using a server at home with a
cheap module NEO-6M and also one with SAM-M8Q. For comparsions effect i've
put the NEO-6M to compare the ntp time of the rpi that this receiver is
connected to with the server from the article: you can see in the
thingspeak: thingspeak_channel
<https://thingspeak.com/channels/691405/>

If you want the source code for the 1 PPS generation thats it:
1pps_generation_src_code
<https://github.com/LuizPauloDamaceno/rpi_pps_out/blob/master/ppsout.c>

Best regards,

Luiz

Em seg, 22 de jul de 2019 às 11:05, wildylion via time-nuts <
time-nuts@lists.febo.com> escreveu:

> Hello there,
>
> I wanted to ask for advice regarding NTP
>
> 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?
>
> Situation 2:
> Also, there's a need for more dependable NTP time sources for our
> colocated spaces.
>
> 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.
>
> 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? 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?
>
> Sent with [ProtonMail](https://protonmail.com) Secure Email.
> ___
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe, go to
> http://

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

[K5ROE Mike]

You may want to look at something an Endrun CDMA ntpserver for the 
datacenter; don't need view of the sky. Available on the used market sub $1k


Standard solution for this scenario.


K5ROE Mike

On 7/22/19 10:50 AM, wildylion via time-nuts wrote:

Yeah, of course I will NOT do anything home-grown for the datacenter.

But currently it uses 3 Stratum 2 NTP servers, one per DC, with them 
referencing a list of 4 close-by Stratum 1 sources.

ntpstat generally says that time is correct within ~50 ms, while jitter and 
offset generally don't exceed 1ms, the root dispersion is quite large.
Also these Stratum 2 NTPs are run from Cisco routers, which I doubt are very 
good at timekeeping.

When I implemented this scheme, I offered to have S2 on a set of x86 servers, 
but was overruled by management who said it'll be better if we run S2's off 
Cisco gear.

So what if we add a couple GPSDO's into the mix, using them as primary time 
sources alongside public Stratum1 NTP servers for sanity check? And of course 
moving the S2's to something more stable.

My own, homegrown S1 pool NTP is another matter entirely - I think just a tuned 
Raspi with a M8N will be enough?

Sent with [ProtonMail](https://protonmail.com) Secure Email.

‐‐‐ Original Message ‐‐‐
On Monday, 22 July 2019 г., 17:38, Taka Kamiya  wrote:


If you have 100 production servers with database, I am going to strongly discourage you 
from taking a "home grown" route.  You will need multiple redundant 
implementation with fail-over.  You mentioned budget.  How much are your bosses willing 
to pay for consultation fees for failed or corrupted data?  I am assuming you are talking 
about Oracle RDBMS with minimum of 2 way RAC.

If you are using collocation services, doesn't the center itself offer ntp 
service for fee?

If you need 24 hour hold-over, I will take nothing less than multiple ovenized 
crystal OSC GPSDO with redundancy per center.  Then feed that into ntp server 
with multi-location fail over.

If I were responsible for managing such system and if my boss will want me to 
go cheap route, I will seriously fight it.  If it's successful, your boss will 
get credit for spending little and getting a big benefit.  WHEN it fails, it's 
going to be your fault for not mitigating risk sufficiently.  Try pricing out 2 
days of consulting fees

---
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG

On Monday, July 22, 2019, 10:05:56 AM EDT, wildylion via time-nuts 
 wrote:

Hello there,

I wanted to ask for advice regarding NTP

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?

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

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.

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? 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?

Sent with [ProtonMail](https://protonmail.com) Secure Email.
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Re: [time-nuts] Noob question, NTP stratum 1.

[wildylion via time-nuts]

Alright, I agree.

The point is: do we ever need S1 NTPs? I think, this could be a nice addition 
if properly realized, but right now I'm not sure if I can propose it.

Anyway, going to plan moving these NTPs from the Cisco gear (where they didn't 
belong from the start, anyway).


Sent with ProtonMail Secure Email.

‐‐‐ Original Message ‐‐‐
On Monday, 22 July 2019 г., 22:01, Mike Cook  wrote:

> .
>
> > 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? Of course, all the NTP infrastructure will be 
> > monitored, and possibly we'll use Stratum 2 servers which would be slaved to
>
> Your management needs educating. Your whole network architecture needs to be 
> analyzed . What happens if a S1 server goes away , what happens when a switch 
> dies , or a router…….
> 2 clocks is a bad idea. 2 clocks from the same manufacturer is a worse idea. 
> If there is a FW issue in one it will get the other.
>
> > GPSDO S1's AND the public NTP pool for sanity checks.
> > Maybe BG7TBL's units instead of LeoNTP?
> > Is that a good idea?
> > Sent with ProtonMail Secure Email.
> >
> > time-nuts mailing list -- time-nuts@lists.febo.com
> > To unsubscribe, go to 
> > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> > and follow the instructions there.
>
> « What’s the point? »
> J.C.



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

[Paul Theodoropoulos via time-nuts]

On 7/22/19 07:50, wildylion via time-nuts wrote:

So what if we add a couple GPSDO's into the mix, using them as primary time 
sources alongside public Stratum1 NTP servers for sanity check? And of course 
moving the S2's to something more stable.


Will you have access to a good location for the antenna? colo spaces 
typically have a maze of cable runs, air handlers, etc above the space, 
not to mention metal the cabinets themselves - it could be very 
difficult to get a good gps signal.


--
Paul Theodoropoulos
www.anastrophe.com

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

[Paul Theodoropoulos via time-nuts]

On 7/22/19 11:52, Achim Gratz wrote:

Well, I have jitter (PPS timestamps) within ~2µs and the occasional
"hair" that goes out to about 30µs.  The distribution is a little bit
wider on the three systems that are loaded with extra server tasks, but
not much.  The thing to note is that you need to boot with "nohz=off",
set a fixed frequency as high as possible and use an interval timer for
controlling the CPU load (I use all four cores as workers and adjust
them at 40Hz).
Yes, nohz off is necessary for sure. I use a  bunch of assorted tweaks 
and am able to keep RMS time jitter under 300ns at 95th percentile in a 
given 24 hour interval. However, it takes very, very, *very* little user 
(me) activity on the device  itself to cause larger spikes into the 
microsecond realm. I upgraded my devices from Raspbian Stretch to Buster 
over the weekend, causing a spike to 3 microseconds offset. However, 
offsets have settled in even lower since the upgrade.


I use,among other things, partrt to set up 'realtime' cpu partitioning, 
and schedtool to nail ntpd to core 3 and gpsd to core 2 - but I suspect 
any improvement I see probably falls into the psychosomatic realm. ;)


Disabling as many cronjobs and running services as possible provides by 
far the most benefit to stability. Oh, and staying off the command line!


--
Paul Theodoropoulos
www.anastrophe.com

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

[Kasper Pedersen]

On 22/07/2019 18.46, Achim Gratz wrote:
> Tim Shoppa writes:
>> The Raspberry Pi processor clock, like any motherboards', will often be off
>> by off anywhere from +/-200ppm but the good news is that it usually varies
>> by less than +/-10ppm over a day and ntpd does a good job tracking this and
>> using the drift correction during no-signal periods.
> 
> All rasPi I've bought so far (5 of them, all different models from three
> different sources) were ~10ppm slow at RT and within -6ppm and 0ppm at
> the apex temperature point of the crystal (around 60°C).  It is possible
> to keep the temperature within about 0.2K of that point by using the CPU
> itself as a heater and thermometer and the resulting frequency within
> +-20ppb over a day when disciplined via pps-gpio.  The residual drift is
> initially positive and gets smaller over time, mine are down to about
> 20~30ppb per week.

Regarding the massive offsets that sometimes come up, it is worth asking
when that 'truth' was learned, and with how old a kernel, if Linux was
involved.

Pre-2011, and if Debian was involved probably pre-2018, there was a
rounding error in the kernel, causing the clock code to miscount by a
lot (127 ppm) on most motherboards, and worse on boards with better
timer resolution.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.3-rc1=a386b5af8edda1c742ce9f77891e112eefffc005

After this, the offsets on all the machines I had became a lot more
realistic*. Putting together a crystal oscillator and pulling it so that
it is 200ppm off, and reliable for manufacturing, is actually hard.

As to reliable NTP: Over the past ~17 years I have learned that every
receiver will fail at some point, all receivers of a brand will fail at
the same time, and you need to plan for that.

/Kasper Pedersen

*There remains an error of typically 2 ppb after the patch, but I was
short on time.

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

[Achim Gratz]

Paul Theodoropoulos via time-nuts writes:
> I've also found that my Raspi's give the best results with board temp
> right around 60°C. However, I found that the 'CPU as heater', while it
> does help dramatically compared to nothing at all, it introduces a lot
> of jitter on its own. Much better results by keeping them in an
> insulated enclosure in a relatively stable location (for me, a
> closet!), and 'tuning' the insulation as needed to balance venting
> against retention.

Well, I have jitter (PPS timestamps) within ~2µs and the occasional
"hair" that goes out to about 30µs.  The distribution is a little bit
wider on the three systems that are loaded with extra server tasks, but
not much.  The thing to note is that you need to boot with "nohz=off",
set a fixed frequency as high as possible and use an interval timer for
controlling the CPU load (I use all four cores as workers and adjust
them at 40Hz).

[I can post plots, but at ~500kiB I think I should rather ask for
permission first.]


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Waldorf MIDI Implementation & additional documentation:
http://Synth.Stromeko.net/Downloads.html#WaldorfDocs

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

[Paul Theodoropoulos via time-nuts]

On 7/22/19 09:46, Achim Gratz wrote:

All rasPi I've bought so far (5 of them, all different models from three
different sources) were ~10ppm slow at RT and within -6ppm and 0ppm at
the apex temperature point of the crystal (around 60°C).  It is possible
to keep the temperature within about 0.2K of that point by using the CPU
itself as a heater and thermometer and the resulting frequency within
+-20ppb over a day when disciplined via pps-gpio.  The residual drift is
initially positive and gets smaller over time, mine are down to about
20~30ppb per week.
I've also found that my Raspi's give the best results with board temp 
right around 60°C. However, I found that the 'CPU as heater', while it 
does help dramatically compared to nothing at all, it introduces a lot 
of jitter on its own. Much better results by keeping them in an 
insulated enclosure in a relatively stable location (for me, a closet!), 
and 'tuning' the insulation as needed to balance venting against retention.

I've never tried to hold over since it's really hard to figure out when
to start holding and when to switch back.  A 24 hour holdover is pretty
severe, but I guess you could keep it within double-digit ms territory
without getting too fancy if you've got that right.

Instead, by having enough independent NTP servers (all with their own
antenna) the clients figure out by themselves when one is off by more
than about a millisecond and switch to another one.  Each server
monitors the other ones and if it finds itself off from that bunch too
much will drop down from stratum-1 to stratum-2.  When exactly that
happens depends a bit on how fast the drift rate is, but usually between
3ms and 5ms.
Something that just occurred to me, and I'm curious if I'm off in the 
weeds here - while a GPS failure could take many forms, I wonder if 
there's a good argument to be made to having at least one or two peers 
who are geographically quite *far* from one's location - e.g. the other 
side of the world - to at least ensure that some number of satellites 
might be available when others might not. Thinking in terms of a 
Carrington event scenario. Wouldn't the GNSS on the far side of the 
earth possibly fare better in such an event - all other things being 
equal? I guess it would depend on how long it took for the mass ejection 
to pass the earth.


Yeah, I think I'm off in the weeds.

While I support that sentiment, after initial problems with off-brand
cards the ones I have now are all getting into their third year with no
signs of problems (knocks on wood).  In a datacenter you'd almost
certainly net boot the rasPi instead of giving them a microSD card.

I can echo that sentiment re SD cards. I'm running Samsung EVO Plus and 
Sandisk Ultra cards in my devices, never a problem. Considering that the 
'sweet spot' for pricing on SD cards is now the 32gb ones, it provides a 
great buffer for the controller to handle internal block allocation for 
longer life.


--
Paul Theodoropoulos
www.anastrophe.com

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

[Luiz Paulo Damaceno]

Dear colleagues, i've made some tests and wrote an article about Raspberry
Pi as a timeserver. I think we can trust on it and this board can keep a
good time from GNSS PPS. I'm open to suggestions. I hope this can help in
the decision making process. The link: rpi_article


Also, in our tests as you can see in the article, for general purposes the
RPI has a good dealing with high loads. The difference is we've removed the
crystal oscillator and put a signal from a synthesizer, you can keep the
crystal and trust on pps signal too. I'm using a server at home with a
cheap module NEO-6M and also one with SAM-M8Q. For comparsions effect i've
put the NEO-6M to compare the ntp time of the rpi that this receiver is
connected to with the server from the article: you can see in the
thingspeak: thingspeak_channel


If you want the source code for the 1 PPS generation thats it:
1pps_generation_src_code


Best regards,

Luiz

Em seg, 22 de jul de 2019 às 11:05, wildylion via time-nuts <
time-nuts@lists.febo.com> escreveu:

> Hello there,
>
> I wanted to ask for advice regarding NTP
>
> 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?
>
> Situation 2:
> Also, there's a need for more dependable NTP time sources for our
> colocated spaces.
>
> 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.
>
> 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? 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?
>
> Sent with [ProtonMail](https://protonmail.com) Secure Email.
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Re: [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.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

SD adaptation for Waldorf rackAttack V1.04R1:
http://Synth.Stromeko.net/Downloads.html#WaldorfSDada

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

[Achim Gratz]

Tim Shoppa writes:
> Real ntpd uses a drift file to track the local processor's frequency offset
> and has a good estimate of processor clock drift after a day of tracking.

That assumes stable median temperature and predictable temperature
swings.

> The Raspberry Pi processor clock, like any motherboards', will often be off
> by off anywhere from +/-200ppm but the good news is that it usually varies
> by less than +/-10ppm over a day and ntpd does a good job tracking this and
> using the drift correction during no-signal periods.

All rasPi I've bought so far (5 of them, all different models from three
different sources) were ~10ppm slow at RT and within -6ppm and 0ppm at
the apex temperature point of the crystal (around 60°C).  It is possible
to keep the temperature within about 0.2K of that point by using the CPU
itself as a heater and thermometer and the resulting frequency within
+-20ppb over a day when disciplined via pps-gpio.  The residual drift is
initially positive and gets smaller over time, mine are down to about
20~30ppb per week.

> +/-10ppm over 24 hours is about +/-1 second.

I've never tried to hold over since it's really hard to figure out when
to start holding and when to switch back.  A 24 hour holdover is pretty
severe, but I guess you could keep it within double-digit ms territory
without getting too fancy if you've got that right.

Instead, by having enough independent NTP servers (all with their own
antenna) the clients figure out by themselves when one is off by more
than about a millisecond and switch to another one.  Each server
monitors the other ones and if it finds itself off from that bunch too
much will drop down from stratum-1 to stratum-2.  When exactly that
happens depends a bit on how fast the drift rate is, but usually between
3ms and 5ms.

> I would strongly discourage using a Raspberry Pi in any not-just-for-fun
> application.

Indeed.  I'd opt for something like PCEngines' APU line since they have
accessible GPIO and PTP capable ethernet.

> I have had very poor luck keeping even brand-name hi-grade
> microSD cards working for a year in 24x7 Raspberry Pi hardware. No-name or
> store brand microSD cards seem to barely work at all when new.

While I support that sentiment, after initial problems with off-brand
cards the ones I have now are all getting into their third year with no
signs of problems (knocks on wood).  In a datacenter you'd almost
certainly net boot the rasPi instead of giving them a microSD card.

> Unless your server farms are completely isolated from the internet at
> large, you should consider using a curated list of public NTP sources.

The key to NTP reliability is copious redundancy, so you'll certainly
want local servers in addition to that, even if you have redundant
outside connectivity.


Regards,
Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Wavetables for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables

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

[shouldbe q931]

On Mon, Jul 22, 2019 at 5:03 PM wildylion via time-nuts <
time-nuts@lists.febo.com> wrote:

> Yeah, of course I will NOT do anything home-grown for the datacenter.
>
> But currently it uses 3 Stratum 2 NTP servers, one per DC, with them
> referencing a list of 4 close-by Stratum 1 sources.
>
> ntpstat generally says that time is correct within ~50 ms, while jitter
> and offset generally don't exceed 1ms, the root dispersion is quite large.
> Also these Stratum 2 NTPs are run from Cisco routers, which I doubt are
> very good at timekeeping.
>
> When I implemented this scheme, I offered to have S2 on a set of x86
> servers, but was overruled by management who said it'll be better if we run
> S2's off Cisco gear.
>
While one can run most Cisco routers as NTP servers, I would advise against
doing this as they don't have very good clocks, and it adds to the
management plane load.


> So what if we add a couple GPSDO's into the mix, using them as primary
> time sources alongside public Stratum1 NTP servers for sanity check? And of
> course moving the S2's to something more stable.
>
Moving away from the Cisco routers would be my first step.


> My own, homegrown S1 pool NTP is another matter entirely - I think just a
> tuned Raspi with a M8N will be enough?
>
A Pi with a ublox is great fun, unfortunately the clock on the Pi is
"poor", and this is a limiting factor.
https://www.ntpsec.org/white-papers/stratum-1-microserver-howto/

Cheers

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

[David J Taylor via time-nuts]

From: wildylion via time-nuts

Hello there,

I wanted to ask for advice regarding NTP

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?

[]
Maybe BG7TBL's units instead of LeoNTP?
Is that a good idea?
===

I would not rely on e.g. a Raspberry Pi for good short-term timekeeping!

Different beasts!  The LeoNTP is a complete unit, providing a precise NTP 
source out of the box.  It can be powered over its Ethernet connection as 
well.  No other computer is required.  Holder over is specified as: 
"Typically 1-4ms in 24 hours.  Reverts to Stratum 16 after 24 hours with no 
GPS".


Cheers,
David
--
SatSignal Software - Quality software for you
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 



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

[wildylion via time-nuts]

Yeah, of course I will NOT do anything home-grown for the datacenter.

But currently it uses 3 Stratum 2 NTP servers, one per DC, with them 
referencing a list of 4 close-by Stratum 1 sources.

ntpstat generally says that time is correct within ~50 ms, while jitter and 
offset generally don't exceed 1ms, the root dispersion is quite large.
Also these Stratum 2 NTPs are run from Cisco routers, which I doubt are very 
good at timekeeping.

When I implemented this scheme, I offered to have S2 on a set of x86 servers, 
but was overruled by management who said it'll be better if we run S2's off 
Cisco gear.

So what if we add a couple GPSDO's into the mix, using them as primary time 
sources alongside public Stratum1 NTP servers for sanity check? And of course 
moving the S2's to something more stable.

My own, homegrown S1 pool NTP is another matter entirely - I think just a tuned 
Raspi with a M8N will be enough?

Sent with [ProtonMail](https://protonmail.com) Secure Email.

‐‐‐ Original Message ‐‐‐
On Monday, 22 July 2019 г., 17:38, Taka Kamiya  wrote:

> If you have 100 production servers with database, I am going to strongly 
> discourage you from taking a "home grown" route.  You will need multiple 
> redundant implementation with fail-over.  You mentioned budget.  How much are 
> your bosses willing to pay for consultation fees for failed or corrupted 
> data?  I am assuming you are talking about Oracle RDBMS with minimum of 2 way 
> RAC.
>
> If you are using collocation services, doesn't the center itself offer ntp 
> service for fee?
>
> If you need 24 hour hold-over, I will take nothing less than multiple 
> ovenized crystal OSC GPSDO with redundancy per center.  Then feed that into 
> ntp server with multi-location fail over.
>
> If I were responsible for managing such system and if my boss will want me to 
> go cheap route, I will seriously fight it.  If it's successful, your boss 
> will get credit for spending little and getting a big benefit.  WHEN it 
> fails, it's going to be your fault for not mitigating risk sufficiently.  Try 
> pricing out 2 days of consulting fees
>
> ---
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
>
> On Monday, July 22, 2019, 10:05:56 AM EDT, wildylion via time-nuts 
>  wrote:
>
> Hello there,
>
> I wanted to ask for advice regarding NTP
>
> 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?
>
> Situation 2:
> Also, there's a need for more dependable NTP time sources for our colocated 
> spaces.
>
> 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.
>
> 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? 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?
>
> Sent with [ProtonMail](https://protonmail.com) Secure Email.
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Re: [time-nuts] Noob question, NTP stratum 1.

[Tim Shoppa]

Real ntpd uses a drift file to track the local processor's frequency offset
and has a good estimate of processor clock drift after a day of tracking.

The Raspberry Pi processor clock, like any motherboards', will often be off
by off anywhere from +/-200ppm but the good news is that it usually varies
by less than +/-10ppm over a day and ntpd does a good job tracking this and
using the drift correction during no-signal periods.

+/-10ppm over 24 hours is about +/-1 second.

I would strongly discourage using a Raspberry Pi in any not-just-for-fun
application. I have had very poor luck keeping even brand-name hi-grade
microSD cards working for a year in 24x7 Raspberry Pi hardware. No-name or
store brand microSD cards seem to barely work at all when new.

Unless your server farms are completely isolated from the internet at
large, you should consider using a curated list of public NTP sources.

Tim N3QE



On Mon, Jul 22, 2019 at 10:05 AM wildylion via time-nuts <
time-nuts@lists.febo.com> wrote:

> Hello there,
>
> I wanted to ask for advice regarding NTP
>
> 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?
>
> Situation 2:
> Also, there's a need for more dependable NTP time sources for our
> colocated spaces.
>
> 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.
>
> 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? 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?
>
> Sent with [ProtonMail](https://protonmail.com) Secure Email.
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> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
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>
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Re: [time-nuts] Noob question, NTP stratum 1.

[Taka Kamiya via time-nuts]

If you have 100 production servers with database, I am going to strongly 
discourage you from taking a "home grown" route.  You will need multiple 
redundant implementation with fail-over.  You mentioned budget.  How much are 
your bosses willing to pay for consultation fees for failed or corrupted data?  
I am assuming you are talking about Oracle RDBMS with minimum of 2 way RAC.  

If you are using collocation services, doesn't the center itself offer ntp 
service for fee?  
If you need 24 hour hold-over, I will take nothing less than multiple ovenized 
crystal OSC GPSDO with redundancy per center.  Then feed that into ntp server 
with multi-location fail over.
If I were responsible for managing such system and if my boss will want me to 
go cheap route, I will seriously fight it.  If it's successful, your boss will 
get credit for spending little and getting a big benefit.  WHEN it fails, it's 
going to be your fault for not mitigating risk sufficiently.  Try pricing out 2 
days of consulting fees

--- 
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
 

On Monday, July 22, 2019, 10:05:56 AM EDT, wildylion via time-nuts 
 wrote:  
 
 Hello there,

I wanted to ask for advice regarding NTP

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?

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

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.

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? 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?

Sent with [ProtonMail](https://protonmail.com) Secure Email.
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[time-nuts] Noob question, NTP stratum 1.

[wildylion via time-nuts]

Hello there,

I wanted to ask for advice regarding NTP

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?

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

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.

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? 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?

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