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Cluster : Storage > Disks : Understanding disks : What happens when you add larger disks to an aggregate
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 RAID level (RAID4 or RAID-DP) of the aggregate.
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When an aggregate configured for RAID4 protection is created, Data ONTAP assigns the role of parity disk to the largest disk in each RAID group.
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.
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When an aggregate configured for RAID-DP protection is created, Data ONTAP assigns the role of dParity disk and regular parity disk to the largest and second largest disk in the RAID group.
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. Note that 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.
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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