I have 4x2TB LP drives instead. My initial 4 drives have sporadic fail & success SMART test. When I test the unit with real files, it seemed like the drives were degrading randomly. At the very beginning, I was thinking that the 2TB LP drives were not compatible with the unit. Fortunately, for every failure, I marked down the serial # of the failed drives. Very soon, I noticed that there're only 2 serial # repeat over and over again. After replacing the 2 drives, everything works like a charm. Then one week after putting the functional unit to the test, one of the replaced drive failed again. This time it was in the middle of playing a movie. The drive letter disappeared. And the drive never show up on the raid again. It is now about 3 weeks since replacing that drive. Touch wood, everything seems to be working fine.
Consider the initial failure rate of the Seagate drives (3 failures out of 7 drives), at least in my case, don't hesitate to bring them back for replacement. I believe the place you bought the drives will not be surprised to see them back for replacement. On the bright side, there's a 3 years warranty for the drives.
As a side note, the drive failure also allows me to test the RAID rebuild, which is quite straight forward and uneventful.