[clug] October Canberra Linux Users Group meeting
rpeters at pcug.org.au
Wed Oct 21 22:19:45 MDT 2009
On Thursday 22 October 2009 05:00:03 linux-request at lists.samba.org wrote:
> Re: [clug] October Canberra Linux Users Group meeting
> From: Michael James <michael at james.st>
> To: Alex Satrapa <alexsatrapa at mac.com>, CLUG List <linux at lists.samba.org>
> On 21/10/2009, at 3:40 PM, Alex Satrapa wrote:
> > Please bring your laptops and experience/curiosity of virtualisation!
> The biggest problem I've had with virtualisation is timekeeping.
> On real hardware it's been a solved problem since the 90s.
> Run ntpd with a good many servers in a loose network.
> Kept the clocks accurate and was robust, using consensus
> meant any server that went haywire was ignored.
> In virtual bottles having the clock counting ticks doesn't work,
> as the machine isn't there all the time and misses ticks.
> Opensuse and SLES are bad at this, as they run the clock at 1000Hz.
> In a guest, ntpd's assumptions about drift don't hold.
> Running ntpd in multiple guests is an even bigger no-no
> as they seem to fight over the clock.
> ?Does setting the hardware clock in a guest touch the hosts clock?
> Anyway I've tried to run ntpd once in the underlying host OS,
> but I haven't found the way to feed that time up into the guests
> as an absolute value, not ticks that can be mis-counted causing drift.
> My 2 seconds worth,
My VM are just "sandboxes" and I don;t bother with timekeeping. Howver, for
printing I just configure a network printer to the host-attached or other
real network printer.
The hosts get their time from an IPCop ntp server. Seems to me that the same
would work for VM, but might require a port opened if NAT is used between
host & VM. Could then counter drift by more frequent synchronisations and
the guests should not touch the host's clock.
openSUSE handles time synchronisation easily on a native installation -
remains to be seen how NTP client on a guest fares.
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