text: **Disk tier**
  MDisks (logical unit numbers (LUNs)) that are presented to the IBM Storwize V7000 cluster 
  likely have different performance attributes because of the type of disk or RAID array on 
  which they are installed. The MDisks can be on 15,000 revolutions per minute (RPM) Fibre 
  Channel (FC) or serial-attached SCSI (SAS) disk, Nearline SAS, or Serial Advanced 
  Technology Attachment (SATA), or even Flash Disks. Therefore, a storage tier attribute is 
  assigned to each MDisk, and the default is*generic_hdd*. 
  
  **Distributed RAID or DRAID**
  An alternative RAID scheme where the number of drives that are used to store the array can 
  be greater than the equivalent, typical RAID scheme. The same data stripes are distributed 
  across a greater number of drives, which increases the opportunity for parallel I/O and hence 
  improves the overall performance of array. See also “Rebuild area” on page 783. 
  
  **Easy Tier**
  Easy Tier is a volume performance function within the IBM Storwize family that provides 
  automatic data placement of a volume’s extents in a multitiered storage pool. The pool 
  normally contains a mix of Flash Disks and HDDs. Easy Tier measures host I/O activity on 
  the volume’s extents and migrates hot extents onto the Flash Disks to ensure the maximum 
  performance. 