What do you do to mitigate supply risk?

I'm currently in the midst of a study on the effects of cooperative supplier strategies on risk mitigation. Strategies include supplier development, early supplier involvement and so on.. What are your thoughts on the potential of collaboration to reduce upstream risk? Do you have experience or do you rather go for buffering strategies (i.e. building safety stocks, multiple supplies etc.) I'm curious to hear from you! Rgds, Elroy