Mirrored protection: Configuration rules

Here are the configuration rules for mirrored protection.

• Mirrored protection is configured by auxiliary storage pool (ASP) number. The system configures the two units of a mirrored pair within an ASP.
• Mirrored protection requires an even number of storage units for each size of disk unit in the ASP that is being mirrored. An uneven number of storage units for any size of disk unit prevents mirrored protection from starting. This requirement does not apply to disk units that have device parity protection.
• The system attempts to assign the two storage units of a mirrored pair so that a failed unit can be repaired while the system continues to use the other mirrored unit. For a hardware configuration where this is not possible, the repair of the failing unit must be delayed until the system can be powered down. This might be true for a failing mirrored unit which is sharing the same controller or input/output processor (IOP) as its mirrored unit.
• Standard disk mirroring support requires that the mirrored units are at specific input and output addresses on the system. (For Version 3 Release 6, you can override this restriction with a patch.) Both units in the pair must be attached to the multi-function IOP because the system must be able to perform an initial program load (IPL) from either unit. Therefore, the system attempts to assign the mirrored units for unit 1 of the system ASP first. If you are mirroring the system ASP, mirrored protection does not start if valid mirrored units for unit 1 cannot be found.
  Note: Remote mirroring support removes this requirement and provides IOP-level or bus-level protection.