In recent reviews of quotes for HP systems, our Dasher team raised a potential issue of the onboard controller no longer being supported in anything but windows. They provided the following links:
Link to S100i SR SW RAID datasheet: https://h20195.www2.hpe.com/v2/getdocument.aspx?docname=a00019427enw
Link to P408i HW RAID datasheet: https://h20195.www2.hpe.com/v2/GetPDF.aspx/a00008203enw.pdf
They warn that the S100i won't be supported in debian. As such, I requested the above info so we can investigate.