Raid provides
  Economy - several inexpensive disks.
    
  Performance and capacity - multiple disks in parallel.

  Fault tolerance - redundant and hot-swappable.

  - Multiple disks increase chance of failure

  - Optimal performance requires expensive controller.
      

Data parsing - striping.
  Because data is to be spread across several disks, how the data is to be 
  broken up must be considered.
    Data stored in the file sized blocks.

    Data broken into sector/cluster sized blocks distributed across disks.

    Data broken into byte or bit sized blocks distributed across disks.

  Stripe length (or size) - size of data block accessed on a single drive.
    Smaller length distributes files over more drives and should cause faster
      access to each individual file. Better for fast access of large files.
      Paradoxical, because drives accessed at sector/track level, small
         files perform poorly.

    Larger lengths - less parallelism for each file but better for 
      multiple file access. Better for small files with many accesses. 
      Drive tend to function independently.

  Stripe width - determined by the number of drives in system.