Typically, the SATA Drives that are connected to non AMD SATA controller is considered as connected to 3rd party SATA controller and is not support by StoreMI.
Most of the mother boards now a days comes with 2 SATA Controllers. One AMD and and other 3d Party (ex: ASMedia)
There are SATA Ports on mother boards that are mapped to AMD or 3rd Part SATA Controller.
All you need is to look up the board specification, see where are the AMD related SATA ports , connect the SATA drives(HDD/SDD) to it for it to be eligible under AMD StoreMI.
Hope it solved the problem for you.
EX: http://www.asrock.com/MB/AMD/Fatal1ty%20B450%20Gaming%20K4/#Specification (check the "Storage" section" to get to know the available ports, and also look up the board details to find out which SATA port maps to AMD / 3rd party SATA Controller)