text: Storage virtualization allows us to manage the mapping between logical blocks within an LU 
  presented to a host, and blocks on physical drives. This mapping can be as simple, or as 
  complicated, as required by a given use case. A logical block can be mapped to one physical 
  block or for increased availability, multiple blocks that are physically stored on different 
  physical storage systems, possibly in different geographical locations. 
  
  Importantly, the mapping can be dynamic: with EasyTier functionality, IBM Spectrum 
  Virtualize can automatically change underlying storage, to which given groups of blocks 
  (extent) are mapped, to better match a host’s performance requirements with the capabilities 
  of the underlying storage systems. 
  
  IBM Spectrum Virtualize gives a storage administrator a wide range of options to modify 
  volume characteristics: from volume resize, to mirroring, to creating a point-in-time copy with 
  IBM FlashCopy®, to migrating data across physical storage systems. Importantly, all the 
  functionality that is presented to the storage consumers is independent from characteristics of 
  the physical devices that are used to store data. This decoupling of the storage feature set 
  from the underlying hardware and ability to present a single, uniform interface to storage 
  users that masks underlying system complexity is a powerful argument for adopting storage 
  virtualization with IBM Spectrum Virtualize. 