RAID 5 concepts
RAID 5 protection protects data from being lost because of a disk unit failure or because of damage to a disk. RAID 5 protection protects against a one disk unit failure.
If more than one disk fails, you must restore the data from the backup media. Logically, the capacity of one disk unit is dedicated to storing parity data in a parity set. However, in practice the parity data is spread across the disk units. Restoring data to a disk pool that has disk units with device parity protection may take longer than a disk pool that contains only unprotected disk units.
- Systems with IOAs released before V5R2 of OS/400®, the minimum number of disk units in a parity set is 4. The maximum number of disk units in a parity set is 10.
- Systems with IOAs released after V5R2 can have a minimum number of 3 disk units in a parity set. The maximum number of disk units in a parity set is 18.
This table shows how many disk units store parity data within a RAID 5 parity set that is connected to a SCSI IOA.
| Number of disk units in a parity set | Number of disk units that store parity |
|---|---|
| 3 | 2 |
| 4-7 | 4 |
| 8-15 | 8 |
| 16-18 | 16 |
All of the disk units in a parity set with a SAS connection contain parity data.