text: **Introduction to RAID technology**
  RAID technology can provide better performance for data access, high availability for the 
  data, or a combination of both. RAID levels define a trade-off between high availability, 
  performance, and cost. 
  
  When multiple physical disks are set up to use the RAID technology, they are in a*RAID array*. 
  The IBM Storwize V7000 provides multiple, traditional RAID levels: 
  
  (cid:2) RAID 0 
  (cid:2) RAID 1 
  (cid:2) RAID 5 
  (cid:2) RAID 6 
  (cid:2) RAID 10 
  
  In a traditional RAID approach, whether it is RAID10, RAID5, or RAID6, data is spread among 
  drives in an array. However, the spare space is constituted by spare drives, which are global 
  and sit outside of the array. When one of the drives within the array fails the system responds 
  as follows: 
  
  (cid:2) For RAID10, all data is read from the mirrored copy. 
  (cid:2) For RAID5 or RAID6, data is calculated from remaining data stripes and parity. 
  
  Then, the data is written to a spare drive. 
  
  In a disk failure, traditional RAID writes the data to a single spare drive. With increasing 
  capacity, the rebuild time is also increased. And the probability of a second failure during the 
  rebuild process also becomes more likely. In addition, the spares, when they are not being 
  used, are idle, which wastes resources. 