text: The performance is near linear when nodes are added into the cluster until performance 
  eventually becomes limited by the attached components. Although virtualization provides 
  significant flexibility in terms of the components that are used, it does not diminish the 
  necessity of designing the system around the components so that it can deliver the level of 
  performance that you want. 
  
  The key item for planning is your SAN layout. Switch vendors have slightly different planning 
  requirements, but the goal is that you always want to maximize the bandwidth that is available 
  to the Storwize V7000 ports. The Storwize V7000 is one of the few devices that can drive 
  ports to their limits on average; therefore, it is imperative that you put significant thought into 
  planning the SAN layout. 
  
  Essentially, performance improvements are gained by selecting the most appropriate internal 
  disk drive types, spreading the workload across a greater number of back-end resources 
  when using external storage, and adding more caching. These capabilities are provided by 
  the Storwize V7000 cluster. However, the performance of individual resources eventually 
  becomes the limiting factor. 