text: **Implementation considerations**
  Consider the following implementation and operational rules when you use the IBM System 
  Storage Easy Tier function on the Storwize V7000: 
  
  (cid:2) Volumes that are added to storage pools use extents from the “middle” tier of three-tier 
  
  model, if available. Easy Tier then collects usage statistics to determine which extents to 
  move to “faster” T0 or “slower” T2 tiers. If there are no free extents in T1, extents from the 
  other tiers are used. 
  
  (cid:2) When an MDisk with allocated extents is deleted from a storage pool, extents in use are 
  migrated to MDisks in the same tier as the MDisk that is being removed, if possible. If 
  insufficient extents exist in that tier, extents from the other tier are used. 
  
  (cid:2) Easy Tier monitors extent I/O activity of each copy of a mirrored volume. Easy Tier works 
  with each copy independently of the other copy. 
  
  **Note:**Volume mirroring can have different workload characteristics on each copy of the 
  data because reads are normally directed to the primary copy and writes occur to both 
  copies. Therefore, the number of extents that Easy Tier migrates between the tiers 
  might differ for each copy. 