text: **6.1.4 Child storage pools**
  
  A*child storage pool*is a storage pool that is created within a storage pool. The storage pool 
  in which the child storage pool is created is called*parent storage pool*. 
  
  Unlike a parent pool, a child pool does not contain MDisks. Its capacity is provided exclusively 
  by the parent pool in the form of extents. The capacity of a child pool is set at creation time, 
  but can be modified later nondisruptively. The capacity must be a multiple of the parent pool 
  extent size and must be smaller than the free capacity of the parent pool. 
  
  A child pool cannot be created from a data reduction pool. 
  
  Child pools are useful when the capacity allocated to a specific set of volumes must be 
  controlled. For example, child pools can be used with VMware vSphere Virtual Volumes 
  (VVols). Storage administrators can restrict access of VMware administrators to only a part of 
  the storage pool and prevent volumes creation from affecting the rest of the parent storage 
  pool. 
  
  Child pools can also be useful when strict control over thin-provisioned volumes expansion is 
  needed. For example, you might create a child pool with no volumes in it to act as an 
  emergency set of extents. That way, if the parent pool ever runs out of free extent, you can 
  use the ones from the child pool. 