Power outage during Time Machine backup corrupted external hard drive

gshigenaka wrote:

I was backing up (Time Machine) my older MacBook Air to a 5TB external hard drive when it was inadvertantly disconnected from power. The MacBook Air is fine, but the backup drive was corrupted and will not mount via Disk Utility or Terminal. I'm not concerned about the lost backups but I would like to erase/reformat the drive. Everything I have tried will not get it to mount. Is it toast?

You can try Disk Utility>View>Show All Devices I would erase/reformat/initialize as new

Verify you are seeing the Parent drive not Volumes below

There maybe a force mount hold the Option key File>Mount

Erase and reformat a storage device in Disk Utility on Mac

Erase and reformat a storage device in Disk Utility on Mac - Apple Support (CA)