New drive - Volume degraded

That is IF he has a backup!  Not sure why you would have a NAS for awhile with a single HDD.  You have zero protection.  What's the point?  Glad to see that he is finally adding that second HDD, which gives you Raid 1.  Which is bascially a clone/Mirrored of 1 HDD to the other HDD.   

I have 4 3TB WD Red drives and 2 3TB Seagate NAS drives in my 516 NAS.  In fact the 4 WD RED's used to be in my old ReadyNAS NV+ V2 NAS.  It doens't seem to me to be a good idea to pull out both HDD and swap in some type of failed conndition.  When you install a new HDD, it has to format and index the thing which can take HOURS.   I don't know how old your Orignal HDD is.   I've had issues with Seagate drives.  Not holding up and lasting.  When the NAS has to copy and rebuild, it puts extra stress on the drives still in the system.    So you may be getting this error, but it's not from the new HDD, but the orignal HDD.  

Maybe some of this can help

https://community.netgear.com/t5/Using-your-ReadyNAS/Data-Degraded-but-Volumes-are-fine/td-p/1023459

https://community.netgear.com/t5/Using-your-ReadyNAS/Volume-Data-degraded-error/td-p/1207091

Thanks for the reply, cpu8088.

Before I do something silly and loose any data, I need to:

   - Backup, by existing Shares using the 'Backup' tab.

   - Reset factory defaults - How-do-I-access-the-boot-menu-on-my-ReadyNAS

   - Alloy to resync

   - Restore data from backup

Is that right?

Thanks.