We're running VMs as NTP servers in several places, and our
experience has been that it works fine under normal circumstances, but
things get out of sync (at least temporarily) when a vMotion operation
occurs.
I haven't had time to do any significant research into this, but have
considered setting "Latency Sensitivity" to High in VMware, which should
ensure that the memory is reserved (so the balloon driver doesn't try to
clear cache or make things swap in the VM) and a PCPU is 100% allocated
for each VCPU on the VM (which should be OK since the NTP VMs only need
one VCPU, and we have many cores on a host). The idea here would be to
avoid things going badly if the host gets busy.
Several of the hosts which we run NTP servers on aren't running DRS
in fully automated mode, but if we did, I would likely tell DRS to try
to keep the NTP VMs on designated hosts to avoid them being shifted
around for load balancing.
VMware is the only VM environment I have deployed right now, so I
can't say how it works in other hypervisors.
-- Brian
On 04/04/2016 11:18 AM, Jeremy Charles wrote:
I’m seeing all sort of documentation about how it’s not a great idea
to use a VM as an NTP server due to how sketchy time tracking is
within a VM.
My supervisor directed me to try it anyway. He feels that our
existing NTP servers are too old and need to be replaced, and he wants
to replace them with VMs rather than physical servers.
I’m not seeing any difference in behavior between the two existing
physical NTP servers and the VM that I set up to test as an NTP server.
Thoughts?
==
Jeremy Charles
Epic’s Computer and Technology Services Division
jchar...@epic.com
608-271-9000
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