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, 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.

1. 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.

2. 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.

Table 1. Number of disk units that have parity with SCSI IOAs

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

• How RAID 5 works
  This topic describes how device parity protection works.

• Elements of RAID 5 protection
  This topic describes and illustrates RAID 5 protection.

• How RAID 5 affects performance
  Learn about how performance is affected when using RAID 5 protection.

• Benefits of RAID 5 protection
  There are many benefits of using RAID 5 device parity protection.

• Costs and limitations of RAID 5 protection
  There are costs and limitations when using RAID 5 protection.

• Parity set optimization for RAID 5 protection
  When you select to optimize a parity set, the IOA will choose disk units for parity sets according to the optimization value you have chosen.

• Read operations on a failed disk unit
  To access the data that was contained on a failed disk unit, device parity protection must read each disk unit in the parity set that contains the failed disk unit.

• IOA migration
  There are considerations and limitations when migrating an IOA.

 

Parent topic:

Device parity protection concepts

Related concepts
Basic disk pools Mirrored protection Benefits of geographic mirroring

Related tasks
Creating a disk pool Adding a disk unit or disk pool

Related information
Backup and Recovery