ESXi host takes longer time to sync with NTP

Products

• VMware vSphere ESXi

Issue/Introduction

Although NTP configuration is set at minpoll 6 and maxpoll 6, sync takes around ~200 seconds to complete 

#watch esxcli system ntp get 

 Enabled: true
  Loglevel: warning
  PID: 1171389
  Runtime Seconds: 2
  Servers: time1.google.com minpoll 6 maxpoll 6 
  Service Providing Kernel Time: Network Time Protocol
  Time Service Enabled: true
  Time Synchronized: false

 Enabled: true
  Loglevel: warning
  PID: 1171389
  Runtime Seconds: 190
  Servers: time1.google.com minpoll 6 maxpoll 6   
  Service Providing Kernel Time: Network Time Protocol
  Time Service Enabled: true
  Time Synchronized: true

Environment

VMware ESXi 7.x

VMware ESXi 8.x

Cause

• The minpoll settings are not defined for quick sync process, rather more persistent synchronization through out the lifetime of the NTP server. 
• When minpoll is set to 6, the sync happens in an interval of 2^6 =64s. Since the sync completes in ~200 second, the iterations to complete the sync is ~200/64 =~3.14. 
  • Note minpoll 6 is also the default, hence even if minpoll is not exclusively set, the time taken to sync will be the same. 
• The lowest value for minpoll can be set to 3 (2^3=8), and the sync should happen at around 25 seconds, which means 25/8 =3.125. 

Resolution

• To speed up the initial sync process it is recommended to use iburst which completes the sync in 8 seconds. 
  • Please refer to the KB : Leveraging the "iburst" Option for Faster ESXi Time Synchronization with NTP for setting up the NTP config with iburst. 
• To change the sync interval throughout  the NTP service lifetime, minpoll and maxpoll config configured based on the requirement in infra. 

Additional Information

For details on the minpoll and maxpoll config, refer : Poll Process