Huge timedrifts when running under KVM

Keiichi · #1 (**permalink**) 02-17-2009, 09:29 AM

I'm running ASG 7.306 in a virtualised environment with linux KVM. The timedrift I experience are quite huge. (10 secs on 30 minutes)

With the ntp function I can't seem to catch up, it seems ntpd only syncs when it's started and never again.

Other KVM guests are experience these timedrifts, so I don't blame it on KVM.

Are there ways to keep the timedrift to an absolute minimum? (Kernels of other guests are compiled with KERN_HZ=100, probably this is an issue)

BarryG · #2 (**permalink**) 02-17-2009, 08:44 PM

You might be able to pass parameters such as KERN_HZ=100 in through the bootloader (e.g. GRUB).

Otherwise, you could try hacking the NTPd settings to sync more often.

Barry

James Bourne · #3 (**permalink**) 02-18-2009, 01:42 AM

KVM? Keyboard/Video/Mouse?

Are you using Virtual Infrastructure 3? VMware Server?

I noticed the VMware image shipped for 7.306 is in an old mode (4) and ships legacy VMware tools. These must be updated to work correctly.

Generally, you should never perform a time sync using an NTP client on a VM. Time synchronisation is always handled by VMware Tools accepting time updates from the underlaying host. This is because the clock calculations are generally incorrect since the number of ticks presented by the virtualised hardware is not necessarily the same as the number of ticks presented by the physical hardware. Here's the best practices guide:

http://www.vmware.com/pdf/vmware_timekeeping.pdf

So if you are using ESX, you need to configure NTP on the ESX host itself and let the time be replicated to the guest: Installing and Configuring NTP on VMware ESX Server

If you are using Server you need to configure NTP appropriately for the host (w32time service on Win and NTPD on Lin syncing against the lowest stratum NTP servers in your region as source from pool.ntp.org). Again ensure you have the latest VMware tools client installed.

Lastly, ensure NTP is disable in your ASG VM.

Hope this helps!

BarryG · #4 (**permalink**) 02-18-2009, 03:08 AM

KVM is a linux-based VM system, not related to VMWare.

Barry

James Bourne · #5 (**permalink**) 02-18-2009, 08:14 PM

Interesting ... not seen that one before. I must give it a go!

Keiichi · #6 (**permalink**) 02-19-2009, 07:46 AM

Quote:

Originally Posted by BarryG

You might be able to pass parameters such as KERN_HZ=100 in through the bootloader (e.g. GRUB).

Otherwise, you could try hacking the NTPd settings to sync more often.

Barry

That's not possible, there's no kernel argument to set this. It's even hardcompiled into the kernel.

I've spend several hours into hacking ntpd, but without any success. No matter what I try or do, the ntpd only syncs it's time once.

jeff.mcgurk · #7 (**permalink**) 06-16-2009, 04:13 PM

I'm also seeing huge time drift running the official 7.4 virtual machine under VMWare Server. I'm running Server 1.08, and OP is running KVM, neither of which are listed as supported environments in the docs. Could this be the issue?

The VMWare documentation on time sync says

Quote:

VMware Tools clock synchronization has a serious limitation: it cannot correct the guest clock if it gets ahead of real time (except in the case of NetWare guest operating systems).

That's exactly what's happening to me. The clock ends up a week or more into the future making logs very difficult to understand. I've tried recommendations in other threads such as editing the vmx with tools.syncTime=TRUE and the config.ini with cpukHz and noTSC settings. Nothing has worked so far.

jeff.mcgurk · #8 (**permalink**) 06-21-2009, 01:00 AM

So I installed VMWare Server 2 and my time drift has stopped. I'd recommend the OP run ASG under a supported virtualization environment to fix this issue.