install os on internal flash or sata drive or both?
I have a late 2013 iMac and the mechanical part of the fusion drive died. I have had the hard drive replaced and now have 2 drives:
121gb Flash Drive (named Untitled)
4TB SATA Drive (named 4TB)
the flash drive has Mohave installed and the 4TB is empty.
My question is should I leave the OS on the Flash Drive, and leave the 4TB for data?
Install an OS on just the 4TB or on both drives?
or rejoin the drives as a fusion drive as it used to be before the replacement? (if that is possible).
And finally is it advisable to upgrade this mac to Catalina?
Thanks in advance for any replies.
iMac 27″, macOS 10.14