Selecting the check box indicates that the aggregate will use double parity disk protection.
Using double parity provides disk protection against single or double disk failure within a RAID group. You need to have at least three disks in a RAID DP group: one or more data disks and two parity disks. For example, a three-disk aggregate could be parity-protected even if one data and one parity disk failed.
In case of single or double disk failure, Data ONTAP replaces the failed disk or disks in the RAID group with one or two spare disks and uses the parity data to reconstruct the data of the failed disks on the replacement disks.