[Beowulf] using extend-reach IB?

[Mark Hahn]

I've got an situation where a 20-25M IB cable would be very handy,
and as far as I can tell, such cables exist.  What's not clear to me
is how they work - I think they all have some form of active components.
some appear to be copper; others fiber, but all seem to draw a few Watts.

I guess they draw from both ends, but do most IB NICs and switches 
support this?  in my case, I have the usual mellanox infinihost III
cards and Voltaire ISR 9024D-M.

alternatively, do you have any experience with media-converters?

the long story is that I would like to drive some display hardware
in an adjoining room from a parallel rendering cluster at one end of a
machineroom (the wrong end, naturally).  it seems quite expensive to
extend dual-link DVI for the total distance (35M or so), so I was 
hoping to extend the DDR IB about 20M to the edge of the machineroom,
then use plain old 15M DL-DVI cables for the rest.  mixed display 
targets, but including one of the new quad-HD panels (3840x2160,
which needs 2x dual-link or 4x single-link.)

thanks, mark hahn.