text: The grain size is defined when the volume is created. The grain size can be 32 KiB, 64 KiB, 
  128 KiB, or 256 KiB. The grain size cannot be changed after the thin-provisioned volume is 
  created. The default grain size is 256 KiB, which is the preferred option; however, the 
  following factors must be considered when deciding on the grain size: 
  
  (cid:2) Smaller grain size helps to save space. If a 16 KiB write I/O requires a new physical grain 
  to be allocated, the used space is 50% of a 32 KiB grain, but just over 6% of 256 KiB grain. 
  If no subsequent writes to other blocks of the grain occur, the volume provisioning is less 
  efficient for volumes with larger grain. 
  
  (cid:2) Smaller grain size requires more metadata I/O to be performed, which increases the load 
  on the physical back-end storage systems. 
  
  (cid:2) When a thin-provisioned volume is a FlashCopy source or target volume, specify the same 
  grain size for FlashCopy and the thin-provisioned volume configuration. Use 256 KiB grain 
  to maximize performance. 