Assuming the Amiga sees it as a regular hard drive, your limits are the same as for any other Amiga hard drive. Typically 4GB, 8GB, or 127GB, depending on a whole bunch of things like your controller, OS version, file system (FFS, PFS, SFS, etc.), and a slew of various other things.
I think there's a few people who've hacked their Amiga's to support 2TB drives, it all just depends how much work you want to put into it.
