Running High Sierra from an external drive, I used Disk Utility to erase my internal Fusion Drive volume.
This produced separate SSD and HDD devices.
How do I re-fuse them?
IMAC (RETINA 5K, 27-INCH, LATE 2015), macOS High Sierra (10.13.1)
Which of the reinstall methods did you try? That is, <cmd><r>, <option><cmd><R>, or <shift><option><cmd><R>?
At which point in the reinstallation process did it fail? Did you see any error messages? If so, what did it(they) say?
Thanks! That reunited the drives.
On to the next problem: following the linked instructions to reinstall MacOS X results in an installation failure loop (can't install, retry).
Welcome.
Erasing volume split my fusion drive
