When creating a new 3.8 TB SSD-based aggregate, the default RAID type used with ONTAP 9.8 is RAID DP. RAID DP, or RAID Double Parity, is commonly used by NetApp's ONTAP for its ability to provide higher data protection by allowing the system to tolerate two concurrent disk failures. This ensures a balance between performance, protection, and capacity utilization, making it the preferred RAID type for SSD-based aggregates in ONTAP 9.8.