I've tried reformatting them and nothing changed. I've also tried putting a file in each drive before pooling them and again, no change in performance. chkdsk found no issue with each drive. Trying with two other 8TB drives also results in the same failure. I still have plenty of drive letters for windows to use.
For some more background on my system:
AMD FX 8320
Gigabyte 990FXA-UD3
32GB memory (up to 24GB in a dynamic RAM disk)
GTX 1070
LSI 9217-8i
10 8TB HDDs (all of these I want to turn into 16TB virtual drives and then added to the top level pool)
3 16TB HDDs
1 1TB SATA SSD boot drive
The two original disks in question are wired directly to the motherboard and not through the LSI card.
I have attached captures of the chkdsk results for both drives and exactly what happens when trying to create a new pool from the newly created virtual 16TB drive ( Data Delta One V:\ and Data Delta Two U:\ -> DrivePool D:\ )