Storage Space cannot see all my HDD's

I have Windows 10 Pro I just installed on a Dell XPS with 12GB of Ram. I have 3 drives: My OS is on a Samsung SSD. My data is on a 3TB HDD partitioned into D: (Data) and E: (Video). I also have another identical 3TB drive. I used the latter drive as a mirror on Win 7 for my D: and E: drives. I removed the mirror prior to moving to Windows 10. Now all my data is in D: and E: on the “Dynamic” Disk 2.

When I tried to create the Storage Space, the dialog only displayed the Disk 1 and would not let me do a resilient setup because I only had one drive.

Why am I unable to see my other data drive (Disk 2) in Storage Spaces? And, why does it show Disk 1 as a single drive instead of how I have it partitioned?

Hi, two (forgive me) very elementary questions:
a. can you confirm you can see your 2nd 3Tb drive in explorer? (Win 10 is now rather famous for losing drive partitions when installed, usually external drives, sometimes internal).
b. can you configure Storage Spaces when one drive already contains data?

I tried reading a few items on Storage Space, but I couldn't find the answer to that! I guess the answer's out there.. or hopefully someone with experience of this can add an answer.

Good that there's no problem seeing your disks- hopefully it should just be that question.

I suspect the answer to that may be in the yellow box in your 1st post.

Also see:
How to create a storage pool and storage space

1- Connect all the drives you want to participate on Storage Spaces.
2- Open Start, do a search and open Storage Spaces.
3- Click the link Create a new pool and storage space.

4- Select the drives you want to be part of the pool and click Create Pool. It's important to note that all the data currently on the drives will be erased during the process.

- from
How to use Storage Spaces in Windows 10 | Windows Central
That the drives need to be empty isn't really surprising- data written will be processed according to the way you have configured the storage space.