Problem with Ultra 4

All you need to do is power off, remove the old drives, insert the new drives and power on.

This in essence will set the NAS up like the day you bought it.

You can download the logs using Raidar.

I am assuming you have a full back up of your data that you can restore.

After that, what you could do however is to upgrade the NAS to the latest operating system OS 6.

Here is how to do it:

Basic instructions are

1. BACKUP, BACKUP, BACKUP (No need since you have no data)
2. Update the NAS Bios by downloading  http://www.readynas.com/download/addons/x86/4.2/BIOS_Update_Package_0.5-x86.bin
3. Upload it using the ReadyNAS web gui firmware update
4. Download PREPR4TOR6_0.1-x86.bin
5. Upload it using the ReadyNAS web gui firmware update, but do not reboot afterwards (avoids the need to do manual factory resets)
6. Download R4toR6_6.9.3.bin
7. Upload it using the ReadyNAS web gui firmware update
8. After you upload the addon/firmware and reboot, it will update the firmware and start a factory default. 

For links to files see OS6 now works on x86 Legacy WARNING: NO NTGR SUPPORT

As you can see it does a factory default, so all data on the NAS will be lost, but you won't have any anyway.