Hello,
The SATA HDD which you hooked up were they new? In that case you will need format them and mount them (LuCI: System - Mount Points)
You can also check:
https://translate.google.com/translate?sl=cs&tl=en&js=y&prev=_t&hl=cs&ie=UTF-8&u=https%3A%2F%2Fwww.turris.cz%2Fdoc%2Fcs%2Fhowto%2Fnas&edit-text=
and