text: **10.1.1 Easy Tier concepts**
  
  Easy Tier is a performance optimization function that automatically migrates (or moves) 
  extents that belong to a volume between different storage tiers, based on their I/O load. 
  Movement of the extents is online and unnoticed from the host point of view. As a result of 
  extent movement, the volume no longer has all its data in one tier, but rather in two or three 
  tiers, and each tier provides optimal performance for the extent, as shown in Figure 10-1. 