If you want guaranteed compatibility and do not want to buy direct from Dell/Alienware, go to Crucial. Crucial is the retail arm of Micron, and Micron is one of the few companies that actually make DRAM. This means that you are getting it straight from the source, rather than a re-packaged product which is what many other companies sell. You can see the guaranteed parts for the Alienware 15 R4 here: Memory RAM & SSD Upgrades | alienware | alienware notebooks | Alienware 15 R4 | Crucial.com, and Crucial says 2TB storage upgrade is recommended.

An ultrafast PCIe Gen3.0 x4 NVMe OS(C:) M.2 2280 drive is a good upgrade. Compare your selection of NVMe read/write speeds against the current market leader Samsung 970 EVO Plus M.2 SSD 2TB (PCIe Gen 3.0 x4 NVMe 1.3) Review. OWC Aura P12 NVMe M.2 SSD (PCIe Gen 3.1 x4 NVMe 1.3) Review. 

The the drive should run just fine in that system.  And OWC has a very good reputation for support, so on the very slim chance the drive does not work, they will likely allow its return.  

Be sure you do not boot the system with both the original and cloned drive in the system the first post-clone bootup.

You know alot about this stuff @ejn63 .

Thanks for the info. I installed and formatted the drive in the 2nd NVMe slot, and the R4 can see it just fine.

I decided to use Acronis True Image to clone the C drive, and I then ran in to a bit of a problem: I can select my 256 Gb C drive as a Source, but the new 2 Tb drive is greyed out as the Destination. Possibly because it's installed internally on the same RAID bus? I also ordered an Express 4M2 which I will be using as an external drive but at the moment is empty. I'll try putting the 2 Tb drive in this and see ATI can see it.

-thanks, Mark

Have used Acronis True Image OEM and this is very good at creating a clone. There is no requirement to format the new drive, Acronis will do everything. As you are having problems, open Disk Management, right click on new drive to get its properties, Partition Format should be GPT (GUID Partition Table). Open Acronis True Image OEM again, open its video help guidance, and take time to understand how to create a clone. Remember to F2 check BIOS, Enable Boot List Option UEFI. 

The OP says single OS(C:) drive, so there is no RAID bus problem? 

Hi Crimsom-thanks for the reply.

I'm not using an OEM version of ATI; I bought and paid for the full version. When I installed the new SSD I went into Disk Management and did a quick format on the drive. I chose GPD for Partition Format. After that it would show up in Windows Explorer (my PC) as the G drive.

On the advice of a user on the ATI Forum I tried the Add Drive tool, but the same result: the disk is seen but greyed out. ATI also un-formatted the new drive for me and it wasn't showing up in Windows Explorer anymore. I had to reformat the drive and now Windows can see it again. All 3 of my internal drives (256 SSD C drive, 1 TB SATA 7200 drive and the new 2 TB SSD) are on the internal RAID bus. The 1 TB SATA drive is not greyed out under the Clone Destination window, but the 2 SSD's are.

ATI recommends making a recovery boot drive, enable it in BIOS as the boot drive, putting the new drive in the C drive location and the original drive in an external enclosure. OWC forgot to send the Thunderbolt 3 cable with the order, so when it arrives I'll follow their instructions to the letter.

So far I'm disappointed with ATI-it hasn't done a single thing I paid for it to do.

-Mark

I had no problems using free Acronis True Image OEM that came with the new 1TB PCIe Gen3.0 x4 NVMe storage card. My original SATA OS(C:) drive was cloned to a 1TB NVMe OS(C:) drive in a different internal slot. 

If clone cannot be created, use Check Disk to find and fix any file errors on the original OS(C:) drive. If new 2TB OWC storage drive still greyed out, Acronis True Image does not recognise this disk. The new 2TB OWC storage drive has a manufacturing fault and should be rejected. 

Give Macrium Reflect (the free version is fine) a try -- it's easier to use, more reliable and flexible than Acronis True Image is.  At one point I used ATI for everything -- and had problems at points where Reflect has none.

Thanks ejn63 for the tip on Macrium Reflect. I'm going to give ATI one more chance tonight and if it doesn't work I'll try Reflect. The new OWC SSD formats fine and I've written and read a few files from it so I'm pretty sure it's good. I'll post later on how it turns out.

-Mark

https://forum.acronis.com/sites/default/files/forums/178344/Disk%203%20Greyed%20Out%20_0.jpg