> On May 1, 2019, at 9:45 PM, Harlan Stenn <st...@nwtime.org> wrote: > > > > On 5/1/19 5:39 PM, William Herrin wrote: >> On Wed, May 1, 2019 at 12:23 PM Mehmet Akcin <meh...@akcin.net> wrote: >> >>> I am trying to buy a GPS based NTP server like this one >>> >>> https://timemachinescorp.com/product/gps-time-server-tm1000a/ >>> >>> but I will be placing this inside a data center, do these need an actual >>> view of a sky to be able to get signal or will they work fine inside a data >>> center building? if you have any other hardware requirements to be able to >>> provide stable time service for hundreds of customers, please let me know. >>> >> >> You buy a powered GPS antenna for it. Which antenna depends on the cable >> length and type. The amplifier in the antenna amplifies the signal just >> enough to overcome the cable loss between the antenna and the receiver. >> Nice thick cables lose less signal. Dinky thin ones are easier to work with. >> >> You sure you need a GPS NTP server? You understand that if you do, you need >> two for reliability right, and probably at geographically diverse >> locations? If you're not on an air-gapped network, consider syncing a >> couple head-end NTP servers against tick and tock (.usno.navy.mil, the >> naval observatory) and not worrying about it. One less piece of equipment >> to manage, update, secure, etc. > > Two is not a great number. If they disagree, there is no majority > clique to be found. > > Also, there is something to be said for using different models/vendors > for the time sources. If you only have the same model from one vendor > and there is a bug, you can lose all your time sources at once. The > GPS week rollover happens every ~19.7 years, and when that problem hits > is a function of the firmware and a manufacturing date put in the firmware. > > These problems can be mitigated if you have "enough" time sources for > your internal NTP servers and you peer with enough other, possibly your, > servers. > >> Regards, >> Bill Herrin > > -- > Harlan Stenn <st...@nwtime.org> > http://networktimefoundation.org - be a member!
To amplify the points made by Harlan Stenn: Four is a better number locally for ntpd instances. As for different models/vendors for the time sources, I consider the GPS constellation as one vendor so I add multiple internet-connected sources as well to my ntp.conf instances. James R. Cutler james.cut...@consultant.com GPG keys: hkps://hkps.pool.sks-keyservers.net
