There is no specific limitation on hard drive capacity for this enclosure. Both 2.5" and 3.5" SATA I/II/III hard drives are supported, and the maximum capacity is not explicitly limited by the manufacturer. However, the total capacity will depend on the hard drives installed.
According to the information made available by the manufacturer, there seems to be no known limit. However, their in-house tests were apparently carried out with disks of up to 10TB.