[Beowulf] Syslog Server-Traffic

[Chris Vaughan]

Thank you all for the input, it's been very helpful in making my
clustering decisions.

On 5/3/07, Mark Hahn <hahn at mcmaster.ca> wrote:
> > I'm researching setting up a cluster and I'm curious as to whether or
> > not it's a good idea to set up a syslog server.   The question I have
>
> depends on how much syslog activity you have, and whether you care
> to look at it (in one spot).  there _are_ scalable and more robust
> system/event logging approaches, but plain old syslog is pretty good.
>
> > is whether the traffic created from logging is going to slow down my
> > network to the point of poor performance?
>
> a syslog message is normally a smallish UDP packet - say 100 bytes.
> if you have 200 nodes each doing 5 per second, that's still only
> 100KB/s - a pretty small fraction of a server's gigabit bandwidth.
> and if you actually have 5/s, something's probably wrong...
>
> > experiences with logging.  The cluster will have a management network
> > and a computational network.
>
> I'm always skeptical about this advice - it's obvious that it might be good
> in cases where a node sustains a nontrivial stream of management traffic
> (say, NFS traffic using jumbo frames) which would interfere with possible
> latency-sensitive/small MPI packets.
>
> but how often does that happen?  consider that with a non-jumbo gigabit net,
> a full packet is only 15 us more than the ~40 or so for a minimal one.
> further, I observe MPI codes mostly getting packed into full nodes,
> and not interfering with themselves much (distinct MPI and file IO phases
> to the program.).
>
> I could more readily imagine segregating traffic to two nets based on
> packet size or TOS.  or bonding them in the first place.  in any case,
> I think you'd have to work pretty hard to generate enough syslog traffic
> to matter much.
>
> > Greater than 64 Nodes, Yes.
> > Greater than 64 and less than 128, Maybe?
> > Greater than 128 No
>
> for a smallish cluster like 64 nodes, I don't think I'd worry about
> syslog even if the net were just 100bT.  for going above 200 nodes,
> I'd probably try to do some measurements and extrapolation, but the
> numbers above make it look minor.
>


-- 
------------------------------
Christopher Vaughan