The best time to start device parity protection is when you add new or nonconfigured disk units. The Add a disk unit or disk pool has steps for including disk units in a parity set and starting device parity protection. It is also possible to start device parity protection at a later time.
The minimum number of disk units in a parity set is 4. The maximum number of disk units in a parity set is 18.
To learn more about how device parity protection is implemented, see How device parity protection works. Examples: Device parity and mirrored protection shows some examples of how device parity protection can be used in conjunction with mirrored protection.