[ntp:questions] NTP vs chrony comparison (Was: oscillations in ntp clock synchronization)
david at ex.djwhome.demon.co.uk.invalid
Wed Jan 23 23:24:46 UTC 2008
> Chrony is also a server. The key detraction for me is that it cannot use hardware clocks.
That would be a specification violation (should level, I think), as
chrony is only an SNTP implementation. In some "off list"
correspondence with Dave Mills be points out one reason for this is that
the end to end response of an NTP network depends on all steps
implementing the protocol properly. My impression is that, even though
the clock discipline algorithm isn't normative in NTPv3, that includes
using the specified discipline algorithm. I suspect this may be
enforced in the latest version of the specification.
I strongly suspect that the pool server people wouldn't want chroony as
a pool server, although it turns out that someone was running optenntpd
> are better than NTP's are. The key question is how close to the real time
> is the time that the system clock delivers. Chrony is closer by factors of
> at least 2 and probably if run at high priority as my ntp is, much better
You cannot say that except when the system is clearly out of lock, as
you are not measuring the necessary parameter, because to do so would
require special instrumentation.
> I have seen this both with a chrony controlled clock and an NTP controlled
> clock. It is just that the NTP response is not good.
As noted in another article, I suspect what might be needed is a mixed
approach, using the chrony approach to gain or regain lock (whilst
signalling alarm and stratum 16 downstream) with the ntpd approach used
when the loop is locked. However Dave Mills can be particularly stubborn.
More information about the questions