Time Machine greyed out external HD

1. Don't panic!

2. Your backup hard drive has to be excluded from the TimeMachine backup otherwise it would create an infinite loop.

3. Since you already formatted (and erased) on of your disks, make sure your backup hard drive is formatted properly with MacOs Journaled, don't use any FAT-formats.

Read the instructions How to back up your Mac with Time Machine: https://support.apple.com/en-us/HT201250

4. Make a TimeMachine backup onto your recently erased, empty disk.

5. If a timeMachine backup stops, don't erase something. Just try to resume/restart your backup.

6. When finished, make a backup onto the second disk.

sgershen Said:

"Ihave been using time machine for the past couple years with both external drive. everything works as needed. But now as of today my time machine doesnt work.: it starts to backup, then midway through it stops it doesn't complete. [...]But really my issue is my back ups never finish they could do a back up and midway through it just stops and fails but doesn’t give me any errors and never completes a full back up this is where I’m stuck I restarted unplugged deleted the in progress File....[...]"

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Single Bit-Layer:

Does this always stop at the same percentage each time? If so, it may be a single bit layer issue (meaning it always moves on and writes to the most correct sector on the drive). Technical though it may seem, it is time for a new hard drive.

Using the Correct Format:

What is your macOS operating system? Click on the Apple menu, then select: About this Mac. Use APFS for High Sierra (macOS 10.13) and thereafter. If you use the software that cam with your drive, that may not be letting this be read based on compatibility and system settings. So, next time you purchase a new hard drive, format it right out-of-the-box, using the correct format.

Go Here: File system formats available in Disk Utility on Mac

If the issue persists wihout any error message, you can pinpoint the problem with the help of the console.

https://support.apple.com/guide/console/welcome/mac

You don't have to be an expert, just look for the obvious. Recently, I had an issue with time machine taking way too much time. With the help of console I was able to track down the problem to an unimportant file of my hard drive, which I then excluded from my backup (greyed out).