Harddisk installation question about X-RAID2 limitation

Thanks for your advice. But I totally forgot that I should add new disks one by one because my little daughter kept all my attention yesterday. I just added two disks to the slots, the readyNAS system seemed to be frozen because of my mistake and had never response even I pressed the power button for many many times. I tried to access the system by enter the local IP address in Google Chrome and selected "the factory default" in system-setup page. Then the RN104 began to restart and the screen showed the message : the factory default, Please wait... I waited for its reboot for about 20 min, but nothing happened! It seemed that this time the RN104 was really frozen. At last, I unplugged the cable and reconnected it to my RN104. My RN104 began booting and automatically entered to the factory default. The OS6 was rebuilding the volume as X-RAID2 (RAID 5) mode. But once again the system was freezing today when I used the ReadyNAS Remote software to log in and try to access the system. It was very strange! I can not access to the system-setup page this time and also nothing happened when I pressed the power button. I unplugged my RN104 again! After reboot the OS6, everything is ok now. X-RAID2 continued to rebuild the volume from where it stopped. But I am worrying about whether the 2nd system frozen left any error to the volume which is rebuilding by X-RAID2 now. The status page gave me the detail information about 4 disks when I hoover the mouse on the green circle one by one. ATA error count=0. Does that mean that there is no problem on all of my 4 disks?