radiosity rendering speed

How do you tell how many radiosity steps there will be in a render?
(so you can tell how long it’s going to take)

also, how do people preview the output with yafray, without doing a full render?

couldn’t you have asked that here:
https://blenderartists.org/forum/viewtopic.php?t=21379

what you will need to do is play with the calculation before hand, using the radiosity solver as if you were going to calculate radiosity only once.

Simple really, select all of your meshes with the radio flag, press collect meshes, then go.

You can also see the current radiosity iteration on the console when radiosity is being rendered so that you may judge how far it has gone, this doesn’t help determine what is a good number of iterations though.

and, if you feel incapable of finding tutorials on radiosity settings I point you to the chapters on the topic in the blender 2.0 guide
http://download.blender.org/documentation/NaN_docs/Manual2.0/radiosity.html
http://download.blender.org/documentation/NaN_docs/Manual2.0/RadiosityButtons.html