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User profile for user: Oreocracker
Oreocracker Author
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Mounted external disk, Time machine can't 'see' it.

I am trying to back up on time machine to my external ssd hard drive.

I get a message, 'Back up disk not available, Try backing up again when the external HD is available.'


I've run first aid. It is a USB A.

My main internal HD is partitioned. I don't know if that could be an issue. I only want to copy 1 partition, the main HD. The external HD is not partitioned.


I tried 'Restore' with my main drive, unmounted, remounted and rebooted the machine and that failed as well.



Thank you


Mac Studio

Posted on Jun 4, 2023 10:02 AM

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User profile for user: Bob Timmons
Bob Timmons
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Posted on Jun 4, 2023 12:14 PM

See if what has worked for me might work for you.


Format the backup drive in Mac OS Extended (Journaled), aka HFS+


Restart the Mac and check to see if you can select the drive as a backup destination in Time Machine Settings


If yes, go ahead and start a backup. If an error occurs, try again


If Time Machine can "see" the drive, it will automatically......(and probably without telling you).....format the backup drive as APFS (Case Sensitive) before the backup begins, then the backup will run.


Now, if Time Machine cannot even select the drive as a backup destination, then more work is going to be needed.



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User profile for user: Bob Timmons
Bob Timmons
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Jun 4, 2023 12:14 PM in response to Oreocracker

See if what has worked for me might work for you.


Format the backup drive in Mac OS Extended (Journaled), aka HFS+


Restart the Mac and check to see if you can select the drive as a backup destination in Time Machine Settings


If yes, go ahead and start a backup. If an error occurs, try again


If Time Machine can "see" the drive, it will automatically......(and probably without telling you).....format the backup drive as APFS (Case Sensitive) before the backup begins, then the backup will run.


Now, if Time Machine cannot even select the drive as a backup destination, then more work is going to be needed.



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User profile for user: Oreocracker
Oreocracker Author
User level: Level 1
14 points

Jun 4, 2023 11:49 AM in response to Old Toad

I also tried super duper, and that failed, too. The response from them looking at the log was, "Something's blocking the backup drive from unmounting. Using any antivirus, antimalware, "Clean my..." tool or the like?"

But I can unmount it manually every way possible. So not sure what the problem is.

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User profile for user: Oreocracker
Oreocracker Author
User level: Level 1
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Jun 4, 2023 4:11 PM in response to Bob Timmons

Many thanks. Got another question you might be able to answer. Time machine keeps stopping. I have it on manual, but it stops and I have to constantly continue it. I'm using that USB A so it's got another 11 hours. I have to do it b/c the mac has a faulty port and they may give me a new one this week. Thoughts?

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User profile for user: Bob Timmons
Bob Timmons
Community+ 2025
User level: Level 10
175,442 points

Jun 4, 2023 4:26 PM in response to Oreocracker

Something is wrong. Not sure what. Using USB A, you should be able to back up about 30-40 GB per hour. So, if you have 100 GB to back up it should take about 2 1/2 to 3 hours.


Nothing you can do at this point, since you do not want to stop the backup.

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Mounted external disk, Time machine can't 'see' it.

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