[Beowulf] Spanning Tree Protocol and latency: allowing loops in switching networks for minimizing switch hops

[Rahul Nabar]

Over the years I have scrupulously adhered to the conventional wisdom
that "spanning tree" is turned off on HPC switches. So that protocols
don't time out in the time STP needs to acquire its model of network
topology. But that does assume that there are no loops in the switch
connectivity that can cause broadcast storms etc. Thereby constraining
the network design to a loopless configuration. Most cases this is
fine but.....

In the interest of latency minimum switch hops make sense and for that
loops might sometimes provide the best solution. Just wondering what
people think. Does STP enabled have other drawbacks aside from the
initial lag on port activation? Or maybe all the latency advantage is
always wiped out if the STP being on itself has some massive overhead.

Do you always configure switches to not have loops? Or are loops ok
and then I turn STP ON but just use PortFast to get away with the best
of both worlds.

-- 
Rahul