It's been a while since I've done that on an RN200 NAS, so I'm not sure. The process involves copying every sector on the from one disk to the other disk, so it will take a while.
You should be able to log into the web ui ( https://nas-ip-address/admin ) and see the estimated completion time.
Hopefully, you mean it's doing a RAID sync. Formatting should only take a few minutes.
RAID1 sync on the ReadyNAS takes way longer than it should. You should expect something in the 30+ hour range. You should, however, be able to log into the NAS and see the progress on the Volumes page. If you can't, then there may be a problem with one of your drives.
