I think you mean indentured servant whom was far from being a slave. An indentured servant was given desired passage to a new country or home and, upon completion of his contract, sometimes received a lump sum payment such as a parcel of land and was free to farm or take up trade of his own.
A serf worked under a feudal contract. He was given protection and was allowed property for himself in return for work that he did for his feudal lord. It was possible for a serf to gain favor and rise to a higher class.
In contrast, an african american slave was not allowed to own any property, educate themself, start any enterprise, free themself from slavery and was promised nothing in return for the work he did.
I do not think it is fair to compare african american slaves to the white "slaves" of the medeival or industrial era. The last time there were white slaves comparable to the african american slaves was the ancient era of the roman empire.