How long does it take to build a RAID5 array on a Thecus N4100Pro NAS using four 1TB drives? About 10 hours and 30 minutes. This was with (4) Western Digital Caviar Black 1 TB hard drives, 32 MB Cache, 7200 RPM SATA II (WD1001FALS). I am a big fan of Thecus products! They have been very reliable for me and my family :-).