Trying to load a Windows partition using Boot Camp on an iMac 18,3 with a second internal SSD. This is a carry on from discussion https://discussions.apple.com/thread/250835424?answerId=251765322022.
iMac 27" 5K, 10.15
On a iMac (Retina 5K, 27-inch, 2017) - Technical Specifications, the only storage that can be recognized are
Storage1
1TB Fusion Drive
Configurable to 2TB Fusion Drive or 256GB, 512GB, or 1TB SSD
1TB Fusion Drive
Configurable to 2TB or 3TB Fusion Drive or 256GB, 512GB, or 1TB SSD
2TB Fusion Drive
Configurable to 3TB Fusion Drive or 512GB, 1TB, or 2TB SSD
You have two standalone internal disks. My recommendation is to create an APFS Fusion drive, with the faster SSD as Main and the slower SSD as Secondary. This will use the slower disk as the Windows destination. Be aware that Windows partition cannot be physically larger than the underlying disk used for Windows. Give the current configuration of disks, I suggest using the 500g as Main, and 1TB as Secondary.
Boot Camp Assistant has encountered a problem - An internal error has occurred.
