I clicked 'Start' and let it ran, but it didn't have a progress bar and just had a 'Cancel' button. It says that it detected an error and had the option of automatically fixing it. I then plugged in my WD hard drive to a Windows laptop. I tried changing the Mac laptop, changing the USB cord, same problem. Ever since that my WD hard drive has the flashing problem and can't be mounted on my Mac. When I charged up my Mac again it says that the disk was not ejected properly. I was not actively reading or writing to the external hard drive, but it did have a list of directories open (no individual photo files, but just the directory names). The WD Passport Ultra was plugged into my MacBook on battery.

I tried opening up Disk Utility on my Mac, but it just spins forever trying to mount the external hard drive. It can be read on a Windows laptop (after Windows automatically fixed an error). When I plug my WD Passport Ultra 4TB external hard drive WDBBKD0040BBK-0A (with 2TB of family photos) into my MacBook Pro it has fast flashing of light and can't be mounted. After more than an hour I came back and the drive showed up on my Mac again. I plugged in again into my MacBook and left it there.

Wd external hard drive format for mac