By default, Data ONTAP adds new drives or array LUNs to the most recently created RAID group until it reaches its maximum size. Then Data ONTAP creates a new RAID group. Alternatively, you can specify a RAID group that you want to add storage to.
When you create an aggregate or add storage to an aggregate, Data ONTAP creates new RAID groups as each RAID group is filled with its maximum number of drives or array LUNs. The last RAID group formed might contain fewer drives or array LUNs than the maximum RAID group size for the aggregate. In that case, any storage added to the aggregate is added to the last RAID group until the specified RAID group size is reached.
If you increase the RAID group size for an aggregate, new drives or array LUNs are added only to the most recently created RAID group; the previously created RAID groups remain at their current size unless you explicitly add storage to them.
If you add a drive to a RAID group that is larger than the drives already there, the new drive is capacity-limited to be the same size as the other drives.