Where are the slaves of the Ethiopian Jews?

An entry in Facebook tells about the Ethiopian Jews. They like others in Ethiopia, they too had Sudanese Bantu slaves, that trekked with their masters and families to the Sudan, where they too were all taken to Israel. The writer says that the original Jews do not marry with the slaves even in Israel, and there are cases that the original Ethiopian Jewish recruit refuses to obey orders from an Ethiopian officer of the slave class. I never heard about this but it would be only too human if true. Pic.: The origin of the story.