Question: Corrupt SSD on High Sierra won't unmount
Late 2013 27" iMac on High Sierra. original SSD blade is corrupt due to utility power failures (even w/surge protect). Won't unmount no matter what. Tried Disk Util, recovery methods, Terminal commands, 7 repair programs running it a target drive. Freezes computer connected to it when it mounts. Cannot format as it won't unmount. Turned off spotlight - no luck. Any ideas or clues??
iMac with Retina 5K display, macOS High Sierra (10.13.3), 32 GB Ram