How to add second SSD in Dell Optiplex 3070?

Hello John, did not know that you have created this separate thread and I answered your question on the other thread.  That is fine, I pasted the answer here as well.  If your second drive is not visible and you prefer to change storage controller from RAID to AHCI, your changing from RAID to AHCI should not affect data on either drives.  However, be advised that important data should have been backup externally in case of disaster. 

When changing RAID to AHCI in BIOS settings, the system will be BSOD upon reboot.  Allow the BSOD to cycle twice, on the third reboot, Windows Recovery menu will be displayed.  Select Advanced Repair, Startup Repair, and choose option 4 to boot into Safe Mode.  Select restart from Safe Mode and your system should boot again with AHCI driver enabled. 

Or, you can follow these steps below to change your storage controller driver:

1. Click the Start Button and type cmd
2. Right-click the result and select Run as administrator
3. Type this command and press ENTER: bcdedit /set {current} safeboot minimal
4. Restart the computer and enter BIOS Setup using F2.
5. Change the SATA Operation mode from RAID to AHCI.
6. Save changes and exit Setup and Windows will automatically boot to Safe Mode.
7. Right-click the Windows Start Menu once more. Choose Command Prompt (Admin).
8. Type this command and press ENTER: bcdedit /deletevalue {current} safeboot 
9. Reboot once more and Windows will automatically start with AHCI driver enabled.

Hi Chino,

I am very surprised by the completeness of your advice, rather detailed instructions on how to proceed step by step. I was just expecting reassurance that there would be no systematic loss of UEFI recording, but now I'm looking forward to trying the whole process. I work from home, so computer functionality is important to me. 25 years ago I worked as a technician and server builder, but I don't remember anything anymore.

Thanks again very much for your help!

John

Prague, Czechia