Windows 2019 Server won't boot after adding a HDD

[distortedvision]

I've had this issue before. I have a clean install of WIndows 2019 Server on a HP Proliant Gen8 Microserver.
I installed it with just a SSD.

I then powered it off and added a HDD which is GPT and NTFS formatted with data on it. But it won't boot afterwards and gives error:

"Non-system disk or disk error"

The reason I installed Windows Server without the HDD installed is because it would convert the HDD to MBR and put the System Reserved Partition on it. The problem is I'd lose 2Tb of a 5Tb HDD because MBR only supports 2Tb. It seems ridiculous that you cannot add a HDD afterwards and doesn't seem right to me. It happens before everytime I try to install in this way.

Can anyone help please?

Many thanks!

 

[Neemobeer]

Have you checked the boot order? Sounds like it's simply trying to boot from the other disk