User information for SAS Parity (RAID) sets

Answer

To determine usable GBs of storage when utilizing parity protection, you must understand how IBM i will create parity sets. The IBM i information center should be consulted for complete information. This document offers an overview.

• Available disk space will be reduced by parity data.
• RAID5 always consumes the equivalent of 1 drive per parity set for the parity data.
• RAID6 always consumes the equivalent of 2 drives per parity set for the parity data.
• One or more drives will be set aside if hot spare will be used for RAID protected drives.
• 1 drive set aside for hot spare when 18 or fewer drives are present
• 2 drives are set aside for hot spare when 19 or more drives are present
  

• Parity optimization choice will influence the quantity of parity sets created. Parity optimization choices are balanced (default), performance, capacity, and availability. You can read more about these choices in the IBM i information center (use the search phrase parity optimization).
• Availability – minimize potential failure points. Generally creates the highest quantity of parity sets with the smallest quantity of drives per parity set.
• Performance – provide the fastest data access. And with SAS dual controller configurations always attempts to put the same quantity of drives in an even number of parity sets
• Capacity – used to maximize available GBs, always creates the fewest number of parity sets possible
• Balanced – creates a configuration that is balanced between performance and capacity.
• Parity set rules when the controller is a PCIe or PCI-X 3Gb SAS RAID controller
• RAID5 - a minimum of 3 drives in a parity set, and no more than 18 drives.
• RAID6 - a minimum of 4 drives in a parity set, and no more than 18 drives.

• Parity set rules when the controller is a PCIe2 6Gb SAS RAID controller
• RAID5 - a minimum of 3 drives in a parity set, and no more than 32 drives
• RAID6 - a minimum of 4 drives in a parity set, and no more than 32 drives