Chapter 6. Storage pools 217
Figure 6-35   Single drive failure with DRAID 6 (for simplification, not all packs are shown)
This model addresses the main disadvantages of traditional RAID:
/SM590000In case of a drive failure, data is read from many drives and written to many drives. This 
process minimizes the effect on performance during the rebuild process. Also, it 
significantly reduces rebuild time. (Depending on the distributed array configuration and 
drive sizes the rebuild process can be up to 10 times faster.)
/SM590000Spare space is distributed throughout the array. So, more drives are processing I/O, and 
no spare drives are idling.
IBM Storwize V7000 DRAID implementation has the following additional advantages:
/SM590000In case of a drive failure, only the actual data is rebuilt. Space that is not allocated to 
volumes is not re-created to the spare regions of the array.
/SM590000Arrays can be much larger than before and can span many more drives, therefore 
improving the performance of the array. The maximum number of drives a Distributed 
RAID can contain is 128.
The following are the minimum number of drives that are needed to build a Distributed Array:
/SM590000Six drives for a Distributed RAID6 array
/SM590000Four drives for a Distributed RAID5 array
6.2.3  Creating arrays
Only MDisks (RAID arrays of disks) can be added to pools. It is not possible to add JBOD or a 
single drive. Then, when assigning storage to a pool, the system first needs to create one or 
many MDisks. You cannot create MDisks out of internal drives without assigning them to a 
pool.