The AFF8020 / AFF8040 / AFF8060 / AFF8080EX have min. root volume size of 350 GiB.
The AFF A200 / A300 have min. root volume size of 350 GiB.
The AFF A700s / A700 have min. root volume size of 934 Gib / 962 Gib.
So, if you want to headswap to an AFF A700s / A700, and you had ADP RD2 partitioned root aggregates, and the root aggregate size is less than the minimum root aggregate size - which is 1 TiB - for the AFF A700s / A700, then you might need to add more disk so can you can create a root aggregate big enough to hold the root volume.
Image: HWU for NetApp AFFs with ONTAP 9.3P7-P9