text: When a new MDisk is added to the pool that already has other MDisks and volumes, the 
  system does not immediately redistribute extents that are used by volumes between new and 
  existing MDisks. This task is performed by the Easy Tier feature. It automatically balances 
  volume extents between the MDisks to provide the best performance to the volumes. 
  
  The system decision to turn on Easy Tier for pool movement of extents—between tiers of 
  storage (inter-tier) or between MDisks within a single tier (intra-tier)—is based on the activity 
  that is monitored. Therefore, when you add an MDisk to a pool, extent migration is not 
  performed immediately. No migration of extents occurs until there is sufficient activity to 
  trigger it. 
  
  If Easy Tier is turned off, no extent migration is performed. Only newly allocated extents can 
  be written to a new MDisk. 
  
  For more information about IBM Easy Tier feature, see Chapter 10, “Advanced features for 
  storage efficiency” on page 403. 
  
  To assign an external MDisk to a storage pool with CLI, use the**addmdisk**command. You 
  need to specify the MDisk name or ID, MDisk tier, and target storage pool, as shown in 
  Example 6-25. The command returns no feedback. 