[Beowulf] How to configure a cluster network

[Mark Hahn]

> This reminds me to ask about all the Xen questions.... Virtual machines
> (sans dynamic migration) seem to address the inverse of the problem that
> MPI and other computational clustering solutions address.   Virtual machines
> assume that the hardware is vastly more worthy than the OS and application
> where Beowulf style clustering exists because the hardware is one N'th what is necessary
> to get to the solution.

I don't agree.  virtualization is a big deal because so many servers 
run at low duty cycles (utilization).  VM lets you overlap them in time
while preserving the fiction that they're on separate machines.  this 
is perfect for latency-tolerant operations (like anything involving 
humans...).  virtualization is a throughput thing.

> Where does Xen and other VME (not the system bus) solutions play in Beowulf land.
>
> The "virtual machine environment" stuff will enable CPU vendors to add
> more cores to a box but how does that help/hurt an MPI cluster environment?

throughput or "real" parallel?  it's all about how tight your coupling is.
virtualization is like sharing interconnect links - great if you're 
latency tolerant (that is, loose-coupled, not synchronized), but not if 
your parallel processes need to avoid random delays.