Replace disk in Readynas DUO 1

Thanks, I did it as you said and it works. But now I have another problem, during copying files back to the new drive Frontview stop responding. All other services were OK, copying was in progress, all files were online. I could see NAS in Raidar, but when i clicked Setup I received error 102(net::ERR_CONNECTION_REFUSED). After rebooting NAS it was OK for a while, but now it happens again. Shall I perform factory reset? Is there any test to check health status of NAS (not disks, but memory, etc.)