The Gotek with HxC firmware has a special mode that allows it to be used as a poor's man hard drive. It is accessible via the track 255 [https://hxc2001.com/download/floppy_drive_emulator/SDCard_HxC_Floppy_Emulator_Direct_Access_mode.pdf Source].
This is a great feature as it alleviates the need for another mass storage expansion. And the relative slowness of this solution compared to a proper mass storage device (~10KB/s vs ~50KB/s) is not really much of an issue on Amstrad CPC.
This special Gotek operating mode is supported in [[SymbOS]].