Joined: 14 Mar 2007 Posts: 8657 Location: Back in jolly old England
I don't really know why IBM suggest (i.e. tell you) that the CDS should be single extent, but obviously you have googled and found one example of what may happen. I usually follow the IBM recommendations without very many questions as I believe that they do know what they are talking about.
A multi cluster CDS is when the current CDS will not fit on one volume, or perhaps for performance reasons. It is possible to split a CDS into two (possibly more - but it is a good few years since having had to do this) so you will need DD names such as BCSD and BCDS2 etc. etc.
It is all very well explained in the fine manuals along with the CDS split analyser.