SMT which reposotories??

Hello,

I've just placed an SMT server and mirror just the repositories.
But can someone explain the differences between your individual reposotories?
What should I mirror, because I will not download anything and wants to unnecessarily wasting GB.

What is the differences between
SLES11-Extras
SLES11-Pool
SLES11-Updates
SLES11-SP1-Pool
SLES11-SP1-Updates
SLES11-SP2-Core
SLES11-SP2-Extension-Store
SLES11-SP2-Updates ??

This is my first SMT server and I'm not experienced with SLES and Linux. Therefore, sorry for the simple question ;)

Thanks