[ntp:questions] Is bare metal really better for ntpd? How do I show it?

Dan Geist dan at polter.net
Thu Feb 4 14:56:06 UTC 2016


I'm working on an NTP infrastructure project and trying to demonstrate the benefits of bare metal (vs VMs running the same OS)for commodity lower-stratum servers...but am having a hard time quantifying the difference. 

For example, here are two nodes in the same subnet and with the same upstream servers. The first is on reasonably recent server-class Dell hardware which is otherwise idle. The second is running on a recent ESXi kernel with similar hardware to the first. I have several stratum 3 hosts using both of these as sources and there doesn't appear to be a clear winner in accuracy. If anything, the VM tends to be chosen in source elections more often than not. Also, if you look at the precision below, the bare metal is reporting 2^-22 and the VM is 2^-24.  Am I missing something in my comparisons? Do I need to reduce the variability of the upstream S1 sources to guarantee a more "level playing field" and most importantly, what are the prime indicators of time signal quality when comparing the difference between a hardware PC clock and a virtualized one ?
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root at ntp02# ntpq -pn
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*172.2*.8.33     .GPS.            1 u   21   64   77   14.851    0.018   1.290
+172.2*.0.33     .GPS.            1 u   12   64   77   28.100    0.036   0.609
+172.2*.0.53     .GPS.            1 u   15   64   77   27.023    0.089   2.204
+172.2*.4.33     .GPS.            1 u   17   64   77   27.805    0.019   8.930
 172.2*.0.53     .GPS.            1 u    8   64   77   26.366    0.058   0.272
-172.2*.0.33     .GPS.            1 u    9   64   77   44.638   -3.868   0.178
+172.2*.0.33     .GPS.            1 u    6   64   77   63.905   -0.048   0.202
+172.3*.1.33     .GPS.            1 u    2   64   77   53.065    0.149   0.249
-172.3*.1.53     .GPS.            1 u    8   64   77   60.009    0.383   0.210

root at ntp02# ntpq -c rl
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
version="ntpd 4.2.6p5 at 1.2349-o Wed Nov 11 17:58:54 UTC 2015 (1)",
processor="x86_64", system="Linux/3.13.0-77-generic", leap=00, stratum=2,
precision=-22, rootdelay=15.249, rootdisp=12.094, refid=172.2*.8.33,
reftime=da5de23d.7bd25b22  Thu, Feb  4 2016  9:44:13.483,
clock=da5de27c.d7614550  Thu, Feb  4 2016  9:45:16.841, peer=64360, tc=6,
mintc=3, offset=-0.249, frequency=25.003, sys_jitter=1.187,
clk_jitter=0.679, clk_wander=0.032


[root at ntp03# ntpq -pn
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*172.2*.8.33     .GPS.            1 u   20   64  377   15.426    0.198   0.102
+172.2*.0.53     .GPS.            1 u   65   64  377   27.013    0.071   0.210
#172.2*.0.33     .GPS.            1 u    2   64  377   45.691   -3.602   5.907
+172.2*.0.33     .GPS.            1 u    2   64  377   64.399    0.154   0.233
+172.3*.1.33     .GPS.            1 u   66   64  377   53.187   -0.039   0.673
-172.3*.1.53     .GPS.            1 u   65   64  377   60.901    0.290   0.199
+172.2*.64.53    .GPS.            1 u   66   64  377   19.486   -0.249   0.413
+172.2*.0.33     .GPS.            1 u   65   64  377   28.200   -0.181   0.410
+172.2*.0.53     .GPS.            1 u   65   64  377   27.064   -0.190   0.445

[root at ntp03# ntpq -c rl
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
version="ntpd 4.2.6p5 at 1.2349-o Mon Jan 25 14:27:34 UTC 2016 (1)",
processor="x86_64", system="Linux/3.10.0-327.4.5.el7.x86_64", leap=00,
stratum=2, precision=-24, rootdelay=15.398, rootdisp=3.084,
refid=172.2*.8.33,
reftime=da5de2f1.bbef8015  Thu, Feb  4 2016  9:47:13.734,
clock=da5de312.4aa7b5bd  Thu, Feb  4 2016  9:47:46.291, peer=49919, tc=6,
mintc=3, offset=0.088, frequency=28.576, sys_jitter=0.119,
clk_jitter=0.179, clk_wander=0.033
--------------------------------------------------------------------

Thanks.
Dan 


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