m15 R5, which SSD?

My OS drive only has 256GB so I can install much games and I also do game design and the files are quite large

Hi @Idkwhatmyusershouldbe thank you for sharing update. 

When playing a game it shall be installed on the OS (C:) boot drive, whose free capacity must be large enough to allow all temporary files to be quickly unpacked and used. 

Hi @Idkwhatmyusershouldbe welcome to this free user-to-user Alienware laptop discussion forum. 

The Crucial System Advisor database is a good source of current tested upgrades - Alienware | Memory RAM & SSD Upgrades | Crucial.com. Have a free, no obligation chat with their technical support team. 

Support for Alienware m15 Ryzen Edition R5 (5/4/2021) Storage says the primary drive of your Alienware m15 Ryzen Edition R5 varies with the storage configuration. For m15 R5 with a single M.2 drive, the M.2 drive is the primary drive, or with two M.2 drives, one of the M.2 drives is the primary drive. Dell does not update their 2021 documentation and its tests are limited. 

As your m15 R5 system has two M.2 SSD slots, are you increasing the size of the primary OS (C:) boot drive, or adding a Data storage SDD? 

The Samsung 980 PRO NVMe™ M.2 SSD 500GB interface is PCIe Gen 4.0 x4, NVMe 1.3c. Getting this SSD to make it future proof is debatable, depending on your next purchase. 

Independent Review Alienware m15 R5 Ryzen Edition Laptop Review - More performance for less money - NotebookCheck.net Reviews says Storage Devices: The M.2 NVMe SSD is installed into the PCIe 3.0 x4 slot, but does not manage great results in the benchmarks. However, you will hardly notice the difference to a faster drive when you play games and PCIe 4.0 x4 is not supported, either. 

I am adding another storage ssd for storing large games and files 

Thanks is there any ssd that you recommend for me

So should I just replace the OS drive

Hi @Idkwhatmyusershouldbe thank you for sharing additional information. 

My 17 R5 internal OS (C:) drive is now the 2TB Samsung SSD 970 EVO Plus PCIe 3.0 x4 NVMe 1.3 and RAM memory has been upgraded to be the maximum. My 17 R5 also has two internal 4TB Data storage SSD. 

I will send you the spec tomorrow. Also one more question what if I want to make use of the original OS drive too what do I do

Hi @Idkwhatmyusershouldbe that is a difficult question.

What is your m15 R5 specification? Multiple Alienware m15 Ryzen Edition variants show up online running AMD Ryzen 9 processor and Ampere graphics cards - NotebookCheck.net News.  

Although the m15 R5 has PCIe 3.0 x4 NVMe slots, purchase of PCIe 4.0 x4 NVMe SSD might cost less and/or have increased storage size (more than 2TB). What are your Alienware laptop current use expectations, guess high performance is wanted and on what budget? Best NVMe SSDs for gaming in 2023 | PC Gamer.  Best SSDs 2023: Top NVMe Drives - Tech Advisor.  

Hi @Idkwhatmyusershouldbe thank you for sharing update and question. 

Having installed larger copy of OS (C:) boot drive without the 256GB SSD, the BIOS/UEFI GPT boot list settings are automatically updated. Then install 256GB SSD as Data drive and assign different drive letter. Open Disk Management application to check automatic assignment of 256GB different drive letter or instigate manual assignment, so that Windows OS can use it. How to Open Disk Management (lifewire.com).  

Please remember to have disaster recovery plan, just in case the OS (C:) boot drive becomes irrecoverable. 

the specs are 
Processor AMD Ryzen 7 5800H with Radeon Graphics 3.20 GHz
Installed RAM 16.0 GB (15.4 GB usable)
System type 64-bit operating system, x64-based processor
Pen and touch No pen or touch input is available for this display