I followed Apple's advice to erase my iMac and reinstall macOS to resolve a stratup error. At this point, I have the system running and have downloaded Spotify and Premier Pro. My Mac keeps saying, "disk space is almost full." So I uninstalled Premier Pro to make space and bought more iCloud space. But the notification won't go away. I checked my disk space and found it has only 27.69GB of storage, which was originally 1TB. In Disk Utility, there's only one SSD. The HDD seems to be gone somehow. What should I do?
The HDD portion of your Fusion Drive has likely failed, rendering it not showing up in Disk Utility. The 27.69GB of storage in Disk Utility is your SSD's disk space. Your iMac can't operate with such little space, so it keeps reminding you that you're running out of space.
To ensure your Mac's functionality, you can replace the dead HDD with a new one, then set the Fusion Drive again and reinstall macOS.
Fusion Drive Not Showing Up or Not Working on Mac? Fixed!