Please post a system log that results after having tried to assign one of the disks.
This is old log back in March:
Mar 12 17:14:02 Tower emhttp: shcmd (100): rmmod md-mod |& logger
Mar 12 17:14:02 Tower emhttp: shcmd (101): modprobe md-mod super=/boot/config/super.dat slots=6 |& logger
Mar 12 17:14:02 Tower kernel: md: unRAID driver removed
Mar 12 17:14:02 Tower kernel: md: unRAID driver 2.1.5 installed
Mar 12 17:14:02 Tower kernel: read_file: error 2 opening /boot/config/super.dat
Mar 12 17:14:02 Tower kernel: md: could not read superblock from /boot/config/super.dat
Mar 12 17:14:02 Tower kernel: md: initializing superblock
Mar 12 17:14:02 Tower emhttp: shcmd (102): udevadm settle
Mar 12 17:14:03 Tower emhttp: Device inventory:
Mar 12 17:14:03 Tower emhttp: (sda) 8388608
Mar 12 17:14:03 Tower emhttp: (sdb) 1073741823
Mar 12 17:14:03 Tower emhttp: (sdc) 1073741823
Mar 12 17:14:03 Tower emhttp: (sdd) 1932735283
Mar 12 17:14:03 Tower kernel: mdcmd (1): import 0 0,0
Mar 12 17:14:03 Tower kernel: mdcmd (2): import 1 0,0
Mar 12 17:14:03 Tower kernel: mdcmd (3): import 2 0,0
Mar 12 17:14:03 Tower kernel: mdcmd (4): import 3 0,0
Mar 12 17:14:03 Tower kernel: mdcmd (5): import 4 0,0
Mar 12 17:14:03 Tower kernel: mdcmd (6): import 5 0,0
Mar 12 17:14:03 Tower emhttp: shcmd (103): /usr/local/sbin/emhttp_event driver_loaded
Mar 12 17:14:03 Tower emhttp_event: driver_loaded