We have a Win 2012R2 server that runs (using hyper-v) 3 Windows 2012R2 VMs.
Configuration
- The hyper-v host is configured to sync its time using NTP with
be.pool.ntp.org, see left screenshot - The 3 VMs have the time integration service enabled, and we have disable NTP-synching in the 3 VMs (since this happens using the hyper-v time integration service), see right screenshot
Observation / Problem
However we notice that the time synching is really unstable. Both on the hyper-v host, as well on the VMs (with the VMs drifting from the host).
THe extract below is from the hyper-v host, where yesterday (2016-02-24) we managed to get the time synched to a delta of around 250 ms. However, this morning (2016-02-25 8:40) the delta was already 878 ms.
C:\Users\Administrator>hostname
hyper-v
C:\Users\Administrator>w32tm /stripchart /computer:be.pool.ntp.org /samples:5 /dataonly
Tracking be.pool.ntp.org [85.88.55.5:123].
Collecting 5 samples.
The current time is 2016-02-24 4:55:41 PM.
16:55:41, +00.2644602s
16:55:43, +00.2594171s
16:55:45, +00.2623687s
16:55:47, +00.2591022s
16:55:49, +00.2590253s
C:\Users\Administrator>w32tm /stripchart /computer:be.pool.ntp.org /samples:5 /dataonly
Tracking be.pool.ntp.org [85.88.55.5:123].
Collecting 5 samples.
The current time is 2016-02-25 8:40:18 AM.
08:40:18, +00.8786692s
08:40:20, +00.8781148s
08:40:22, +00.8855366s
08:40:24, +00.8782784s
08:40:26, +00.8779754s
On the VM Billy, yesterday (2016-02-24) we managed to get the same delta as on the hyper-v host (i.e., 250 ms) by restarting the VM. But this morning, the delta was not in sync with the hyper-v host, i.e. delta = 12900 ms. Same story on the other 2 VMs.
C:\Users\Administrator>hostname
billy
C:\Users\Administrator>w32tm /stripchart /computer:be.pool.ntp.org /samples:5 /dataonly
Tracking be.pool.ntp.org [85.88.55.5:123].
Collecting 5 samples.
The current time is 25/02/2016 8:53:13.
08:53:13, +01.2901306s
08:53:15, +01.2903196s
08:53:17, +01.2898293s
08:53:19, +01.2901677s
08:53:21, +01.2904303s
Question
What are we doing wrong? Why is this 'simple' NTP syncing not working? More specifically:
- Why does the hyper-v host have a delta of as much as 800 ms? Do we really need a 3rd part time sync to get reasonable delta's, as suggested here https://serverfault.com/a/394980/25073 ?
- Why are the VMs not in synch with the hyper-v despite having the time integration service turned on (and ntp synch turned off)?
