[Beowulf] Green Cluster?

[fkruggel at uci.edu]

Thanks for your suggestions. Let me be more specific.
I would like to have nodes automatically wake up when
needed and go to sleep when idle for some time. My
ganglia logs tell me that there is considerable idle
time on our cluster. The issue is that I would like to
have the cluster adapt *automatically* to the load,
without interaction of an administrator.

Here is how far I got:
I can set a node to sleep (suspend-to-ram) using ACPI.
But for powering on, I have to press the power button.
No automatic solution.

I can shut down and wake up a node over the network
(e.g., using etherwake). But I consider the time to boot
a node as too long.

Is it possible to wake up a node over lan (without reboot)?
How can I detect that a node was idle for some specific time?

Thanks,

Frithjof