Lenovo ThinkStation P7 Manual page 23

Internal 3.5" bay M.2 kit installation
Another storage option is available via two internal 3.5" drive bay M.2 kits. Up to
two M.2 drives can be installed, given that the following conditions are met:
1. No 3.5" SATA HDDs are installed in the standard slots
2. The front storage FLEX bay is not installed
The location of the 3.5" bay M.2 kits can be seen here:
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