Anyone who has done any research on QNAP products will know that the first digit in the product series indicates how many drives the NAS device can expand to. For our TS-419U, it holds 4 drives. The largest rack NAS device QNAP makes right now is an 8 drive 2U unit. For corporate companies, a 2U may be required but for everyone else the 1U should be more than enough. As we'll detail in this review, the TS-419U can handle 4 internal hard drives and an extra 6 external devices (4 USB and 2 eSATA).