[scyld-users] Re: [Support] Setting up ntpd on compute nodes

Donald Becker becker at scyld.com
Mon Feb 9 19:19:01 PST 2004

On Fri, 6 Feb 2004, Tony Stocker wrote:

> How do we go about setting up ntpd on our compute nodes, with the ntp
> server being the host node?

What aspect of NTP do you need?

This same topic came up during my meeting with Panasas this past Friday:
if you need time synchronization only for the filesystem, our current
approach will work.

We prefer not to run the standard NTP daemon, or any daemon, on compute
nodes. Running daemons on compute nodes results in unpredictable scheduling.
This becomes a significant issue with lock-step computation and
larger node counts, as the slowest node sets the step rate.

Instead Scyld provides 'bdate', which explicitly sets the time
(settimeofday(), including microseconds) on compute nodes from the
master's clock.  This is called at node boot time, and optionally
periodically with 'cron'.  In both cases it follows the Scyld approach
of cluster operation being controlled by a master machine, rather than
compute nodes having independent operations or relying on distributed,
persistent configuation files.

If the exact behavior of 'ntp' is required, it's simple to configure
'ntpd' to start automatically on node boot.  Create a start-up script
that calls
  bpsh -n $NODE /usr/sbin/ntpd -m -g
(or the appropriate options for your needs).

Please let us know what your time sync requirements are -- we can likely
efficiently provide the functionality needed, but are reluctant to
include the 'ntpd' approach in our default node configuration.  It is
more intrusive, complex and configuration-intensive than is needed for a
tightly coupled cluster.

Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
914 Bay Ridge Road, Suite 220		Scyld Beowulf cluster systems
Annapolis MD 21403			410-990-9993

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