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What happens when you add larger disks to an aggregate
What Data ONTAP does when you add disks to an aggregate that are larger than the existing disks depends on the version of Data ONTAP and the RAID level of the aggregate.
For Data ONTAP 8.1 and later, when you add a disk to an aggregate that is larger than the other disks in the aggregate, the new disk is capacity-restricted to be the same size as the smaller disk it replaced, and it is added to the same RAID group a disk of the same size would have been added to.
For earlier versions of Data ONTAP, when you add a larger disk to an aggregate, the result depends on the RAID level of the aggregate:
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When an existing RAID-DP group is assigned an additional disk that is larger than the group’s existing dParity disk, then Data ONTAP reassigns the new disk as the regular parity disk for that RAID group and restricts its capacity to be the same size as the existing dParity disk.
Data ONTAP does not replace the existing dParity disk, even if the new disk is larger than the dParity disk.
Note: Because the smallest parity disk limits the effective size of disks added to a RAID-DP group, you can maximize available disk space by ensuring that the regular parity disk is as large as the dParity disk.
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When an existing RAID4 group is assigned an additional disk that is larger than the group’s existing parity disk, then Data ONTAP reassigns the new disk as parity disk for that RAID group.
Note: If needed, you can replace a capacity-restricted disk with a more suitable (smaller) disk later, to avoid wasting disk space. However, replacing a disk already in use in an aggregate with a larger disk does not result in any additional usable disk space; the new disk is capacity-restricted to be the same size as the smaller disk it replaced.

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