Use secondary SSD slot for operating system?

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Thanks for the several private messages from DELL-Cares indicating that the SSD slot accessible from the SSD drive slot on bottom of the 7760 laptop case cannot be used for a non-operating system drive. 

However, Dell ProSupport is not in agreement.  BIOS change is necessary to direct the boot process to the location of the Operating System drive, as long as drive capacities and interface-type limitations are observed as described here: Precision 7760 Setup and specifications | Dell US.

So, although I have not tried it yet, I should be able to move the O.S. 1tb SSD drive into one of the three open slots and install a strictly data drive into the slot accessible by the access door.  

I currently have these SSD drives purchased from Dell:

• Samsung M.2 2280 1 TB, Gen 4 PCIe x4 NVMe, installed in "secondary slot", accessible via drive access door, and
• VisionTek M.2 QLC 4 TB, Gen 3 PCIe x4 NVMe (containing data only, not yet installed)

Can someone please confirm they're tried moving an O.S. drive into another slot, or guide me on my options to maximize my data storage on this machine? 

You don't say what Bios change means?

It may be the limitation also depends on whether you have a gen3 or primary/boot drive

If you have not installed the new ssd yet you could just test things by downloading the basic install either from the Dell site or Microsoft onto a memory stick, or clone your current os onto your new ssd in a usb adaptor. Then disconnect the old drive and plugin the new one and see what happens.

 Then if it fails make sure you completely erase the drive before you start again.

I don't see why it says you need to have 2 or 4 ssds?

I have just installed 2 TB gen3 ssds in a 7560 which supposedly has the same limitatons of 1TB gen3 ssds as yours.

I am dubious about the helpful Dell guides as they are inconsistent and contradictory with different information in the service manual compared with Teardown guide.

I did play around a lot with the configuration on the Dell purchase site before deciding to take a chance with my 2TB gen3 ssds and some of the configurations I could order were only available if I had a gen4 primary/boot drive, so this may be the key.

@MTNShootR , you can change your OS drive to a different slot and it will boot.  However, you can't hot swap NVMe drives directly from M.2 slot as it is not electrically wired to do so.  You may end up damage your drive or even worse, the motherboard.

NVMe drives can safely hot swap on supported motherboard with backplane and U.2  

Thank your for your Response. 
When you say “you can't hot swap NVMe drives directly from M.2 slot as it is not electrically wired to do so” …

… does that mean that I cannot cold swap these drives and boot on the Samsung? 

• Samsung M.2 2280 1 TB, Gen 4 PCIe x4 NVMe, installed in "secondary slot", accessible via drive access door, and
• VisionTek M.2 QLC 4 TB, Gen 3 PCIe x4 NVMe (containing data only, not yet installed)

 you can change your OS drive to a different slot and it will boot.  However, you can't hot swap NVMe drives directly from M.2 slot as it is not electrically wired to do so.  You may end up damage your drive or even worse , the motherboard.

NVMe drives can safely hot swap on supported motherboard with backplane and U.2.

@MTNShootR , hot swap meant when the computer is powered on and operating system is active, you can remove a data drive and plug in another data drive and the OS will recognize the new drive.

The access door on your system is for convenient and quick access to change/swap your drive.  But you must shut down the power while doing so.  And yes, you can put your Samsung (OS) drive in the primary slot and the VisionTek drive in secondary slot.

Okay thanks for the information @alexpeter23 and @chinodeoro  on hot swapping.  I actually dont need to HOT swap, but only cold swap once power is off.  

My second part of the question is what additional storage type/interface type/capacity  drives can I add, according to the specs?  I am looking to MAXIMIZE data space.  Attached is a screenshot of the Storage section for  7760 specs.  The configuration highlighted in yellow is what I'm confused about.  Given that I already have these drives, (1) what other drives can I install -and- (2) will the 1tb drive be throttled down from 2280 to 2230?

• Samsung M.2 2280 1 TB, Gen 4 PCIe x4 NVMe, installed in "secondary slot", accessible via drive access door, and
• VisionTek M.2 QLC 4 TB, Gen 3 PCIe x4 NVMe (containing data only, not yet installed)

Thanks again everyone for sticking with me on this.  I wish Dell Sales had been more diligent with these requirements 5 months ago...

Hello @MTNShootR , been waiting for a while now but your screenshot is not made visible by Mod yet, so I can't see which highlighted info causing the confusion.  Regardless, I hope my post can help to clear up some of that confusion.

• Dell specs usually listed the SSD type, size, speed which they have tested and supported.  Many users have upgrade their storage with higher capacity and it works for them.  However, you can't demand support from Dell if you get performance issue with those out of specs components.
• NVMe protocol give you higher performance of Read and Write speed than of SATA storage.  However, it produced quite very high temperature during work compare to SATA drive and will require good cooling or else its performance will be deteriorated (throttled).  The newer (PCIe) generation drives produce higher heat (temperature) than the older one.
• Technology is moving at a very fast pace.  What Dell had tested and supported versus the products coming out (or set to come out) in the future will be difficult to say what is the maximum of storage you can put into this system.    
• M.2 is the form factor and the M.2 slots on your motherboard can support NVMe drives, SATA drives, and Optane.  The indication of 2280 or 2230 refers to the length of your SSD.  But the important thing to know is how these slots were wired.  Which one connect to the CPU and which one connect to the chipset.  Your system only has a fixed number of lanes to share across all devices.  They have separate controllers and installing correct drivers can avoid issue and will make them perform optimally.  The more storage (drive) you add in, it will decrease the available lanes for other devices such as your graphics card.

That said, you can upgrade and add in more drives to your system with the consideration of thermal control, the affect of pulling resources from other devices.  Try your 4TB data drive on each slot first and checking the performance.  If you are happy with it, get the NVMe gen.3 SSD in 2280 size, you can add 4TB one at a time until all slots are filled.  Just keep in mind, today maximum is not tomorrow maximum. 

UPDATE: the defective 4tb SSD had been backordered, and it is now due to arrive in about a week. 

My plan is to try this, with someone from Dell that is knowledgeable monitoring my installation:

1. remove the 1tb SSD from the primary slot, move it to a secondary slot

 2. make modification to BIOS to allow system to boot from this 1tb SSD

3. install the replacement 4tb SSD drive into the primary slot. 

4. install the old 4tb SSD into another secondary drive slot

Unfortunately there’s is no concurrence from the Community or from ProSupport whether this will work. I am not comfortable making BIOS changes myself, and I don’t think the 7760 service manual documentation is clear regarding primary/secondary drive configurations or placement. 

So I’m hoping to find someone from Dell that can help do the BIOS update and oversee these drive installations.   

Any advice?  

Hello, I am Muktesh the case owner. I am writing you as i wanted to let you know that dispatch got canceled as the part was not available by the date end-user requested. Please suggest if you are available now to continue the conversation.

I’ve received message from Dell Cares asking to close this ticket. NO, rhe issue concerns documentation which is misleading and confusing. This applies to the 7860 specifications document and the 7760 installation manual. 
This ticket can be closed once Dell responds and corrects those sections of those two documents.

Thank you. Please, quality assurance!