SQL & Oracle backup size limits?

Hi everyone I'm getting dragged into a meeting next week about a issue maybe.

I'm being told there having a issues backing up large DB's SQL & Oracle about 6TB size

Is there a size limit that anyone knows of not sure the process there using yet to backup since its a location I don't look at most of the time.

NBU 7.1

SQL?
Oracle?

what I'm thinking is there doing a local dump and then trying to backup the BAK file for the SQL box and maybe the same for the Oracle stuff also