We have a two, 4 node centera clusters. One being the prod and the other DR, prod replicating to DR. Right now we have 850 GB available capacity left and we are planning to add storage to the cluster. Based on our usage we have estimated to add ~1.2 TB to each cluster. When I add more usable space, do I also need to set aside more disk space to the system and regeneration buffers ? And if we do what percent of the usable space should they be?

Does adding storage mean adding nodes to the cluster? is the process disruptive or it can be done online with the existing nodes up and running?

I appreciate you sharing your experience in upgrading centeras.