Grid5k is giving the possibility to exclusively reserve entire clusters or portions of them for research purposes.
Get to know if you're eligible to get an account and - after obtaining one - make sure to read the usage policy before starting any experiment.
A comprehensive list of available clusters with their characteristics can be found in the Hardware page while in the Network page there are information about their interconnections (how nodes are connected into clusters or - eventually - how different clusters are connected).
Make sure to check the platform status page (only accessible for logged users) to get to know about ordinary or extraordinary maintenance that could eventually slow down or invalidate experiments.