4 ms·
Two observations/questions, the first probably naive: * It's not that hard to get your own "world class" time server, for under a thousand. A Rb standard slav
by loxias 5y ago
Two observations/questions, the first probably naive:
* It's not that hard to get your own "world class" time server, for under a thousand. A Rb standard slaved to a GPSDO is gonna be so accurate and stable, and use that to drive a SBC that supports IEEE1588, where you run your NTP and PTP server. Oh, but I guess that box, while inexpensive, isn't in Amazons DC, so doesn't help you.
* PTP's absence in the Amazon Time Sync Service article is quite conspicuous!
- Gelob 5y agoThem providing PTP would be really interesting
- loxias 5y agoTo be clear, what I meant was "the fact that they're advertising whiz bang time synchronization, but then not using the correct protocol, makes me question the quality of the whole enterprise". Even on local networks, NTP can only get you so close. If you set up chrony just so, in ideal conditions, I've gotten hundreds of microseconds (more commonly ~500-1000us). But combined with PTP, you can get sub-microsecond accuracy.
- travisgriggs 5y agoWhen Microsoft did that kind of thing we called it “embrace and extend.”
- staticassertion 5y agoThat sounds different. Embrace and extend means implementing a protocol and then adding specific non-spec features. For example, postgres 'embraces' SQL and 'extends' it with specific features - in the future postgres could 'extinguish' SQL by breaking from the spec, forcing an ecosystem split.
- loxias 5y agoThank you. I was in the process of writing this exact comment but kept tripping over my own words and eventually gave up.
- pferde 5y agoMicrosoft already does offer PTP on Azure, and nobody calls it EEE. https://docs.microsoft.com/en-us/azure/virtual-machines/linux/time-sync#check-for-ptp-clock-source https://docs.microsoft.com/en-us/azure/virtual-machines/linu...
- deelowe 5y agoAmazon time sync likely also requires extremely accurate clocks on the system board as well to prevent there from being too much drift.
- NavinF 5y agoYou don’t even need a tcxo. If you don’t care about holdover, connecting the pps pin from a $5 GPS module to an $15 SBC will give you a time source that is significantly better than anything you can serve over NTP to your clients. NTP is always gonna be the weak link for a service like this.
- deelowe 5y agoI was referring to the amazon time sync service which I imagine has pretty tight timing requirements (similar to spanner), not NTP. Also, how exactly would GPS work at scale for 10,000s of servers within 1000s of racks within a DC?
- jfrunyon 5y ago"Amazon provides the Amazon Time Sync Service, which is accessible from all EC2 instances, and is also used by other AWS services. This service uses a fleet of satellite-connected and atomic reference clocks in each AWS Region to deliver accurate current time readings of the Coordinated Universal Time (UTC) global standard through Network Time Protocol (NTP). The Amazon Time Sync Service automatically smooths any leap seconds that are added to UTC. "The Amazon Time Sync Service is available through NTP" https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/set-time.html https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/set-time...
- NavinF 5y agoAs I understand it, “amazon time sync service” is just a bunch of NTP servers run by Amazon. Their ClockBound library calculates error bounds the same way you would if you were using a different NTP server: |Local Offset| + Root Dispersion + (Root Delay / 2) >how exactly would GPS work at scale for 10,000s of servers GPS module (+ GPSDO + Rb clock optional) -> SBC running NTP server -> machines running NTP client I’m not sure what you meant by “clocks on the system board” but if you’re talking about the system clock on the NTP server or the NTP client, it really doesn’t matter. Any old crystal on the NTP server is accurate enough to stay locked to a PPS input. The clients are limited by NTP so their clocks don’t really matter either.