Yes, just replace drive 2. When it boots back up it will still give you error messages (degrade mode and a RAID error), just log into the web interfce and click on disk managment > RAID setup. Then click on the orange tab next to RAID Array 1. Just put a check mark next to disk 2 and click on "resynch RAID array". As long as you select "resynch RAID Array" this will not result in data loss. Just don't click "rebuild RAID Array" and you should be fine.