We have summarized the results and organized them by RAID mode for better overview. The four-drive bay Qnap TS-459 Pro is represented by the blue bars in the charts below, while the five-drive bay TS-559 Pro is represented by the green bars.
The HD video recording test consists of 100% sequential data writes, and only really shows a difference in data transfer rates in the RAID 5 mode. In RAID 0 they are quite similar due to the gigabit network port posing a bottleneck. We attribute the marginal differences in test results to measurement margins of error. A similar picture emerges in the RAID 1 mode, with the 2.6 MB/s difference being rather low. The gaps between RAID 5 and 6, at 7.1 MB/s and 8 MB/s, are a bit larger.
The sequential read operations in the HD video playback tests are quite similar. In RAID modes 0, 1, and 5, both NAS devices are at pretty much the same level of performance. The fifth hard drive in the TS-559 Pro becomes valuable in the RAID 5 degraded mode and RAID 6 modes, where the performance benefit speaks in favor of the five-bay version.
There are hardly any noticeable differences in performance between the NAS devices when working with huge amounts of very small files (photo album, four bytes to 102 KB) either. The difference in the RAID 6 mode is lower than when reading or writing sequential data. Only in the degraded version of the RAID 5 mode is the TS-559 Pro able to achieve any higher transfer rates.
More benchmark results can be found in the gallery.