If you accidentally have a power loss when you are still using your external hard drive, and the drive can’t be detected when your Mac is back on.
First you can can hit Cmd + Space and type Disk Utility and choose it.
If you can find your external hard drive on Disk Utility, then pick the partition name, then click the First Aid button on the menu. Wait for a minute then your drive is back.
If you can’t. Then Cmd + Space again and type Terminal. Choose Terminal. Then type diskutil list, enter.
you should see something like this:
⇒ diskutil list /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *251.0 GB disk0 1: EFI EFI 209.7 MB disk0s1 2: Apple_CoreStorage Macintosh HD 250.1 GB disk0s2 3: Apple_Boot Recovery HD 650.0 MB disk0s3 /dev/disk1 (internal, virtual): #: TYPE NAME SIZE IDENTIFIER 0: Apple_HFS Macintosh HD +249.8 GB disk1 Logical Volume on disk0s2 E9DFCD4D-790F-4129-8D56-6CA02CB070BE Unencrypted /dev/disk2 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: FDisk_partition_scheme *1.0 TB disk2 1: Windows_NTFS Mamazo 1.0 TB disk2s1
if you can see your external hard drive, then your disk is probably still good. Mine is on
Now you run:
diskutil unmountDisk /dev/disk2
it will unmount your disk stop any process your hard drive is into. Now you can go to Disk Utility again and do as
There you go.