External hard drive does not mount when I plug it in.

Question

mgs222 Author

Level 1

5 points

External hard drive does not mount when I plug it in.

14" Macbook Pro 2021 running Sequoia 15.5. Apple Silicon.

I plug in an external hard drive and it is not automatically mounted nor is it visible in Disk Utility.

I have tried two drives, two cables, in all three USB ports.

I rebooted the system and the hard drive mounted properly. I was able to make a backup.

Next day the system was back to not mounting the hard drive.

Please suggest possible ways I can fix this problem.

Thanks!

MacBook Pro 14″, macOS 15.5

Posted on Jul 23, 2025 10:14 AM

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Answer 1

Top-ranking reply

Barney-15E

Level 10

123,014 points

Jul 23, 2025 2:37 PM in response to mgs222

The drive is likely, pulling too much current from the USB port and is shutting down the port so it never mounts. That happens with bus power drives all the time as they get older. They start pulling more current as they wear. If you can plug it into a powered hub and it works then that’s the problem.

Sometimes you can use a Y Cable to attach the drive. It has two ends that go into the computer one for Power and one for data.

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Answer 2

Jul 23, 2025 5:05 PM in response to mgs222

there are several possibilities:

• Barney-15E is asserting correctly that the current required is a bit more than can be provided.

• MacOS loads only Mountable Volumes. If a volume is damaged, it can not be Mounted.

Launch Disk Utility,

change its tiny "View" menu to "Show all Devices",

if the physical device appears, it is likely repairable unless it shows a size/capacity of Zero.

choose each in turn and FirstAid/RepairDisk:

the Physical device

the ContainerDisk

each Volume showing.

if any can not be Repaired, try again at least once.

check to be sure the Volume is a type that MacOS supports.

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Answer 3

Jul 23, 2025 2:42 PM in response to mgs222

power available and required (but not actual) can be examined:

Option-Apple Menu > system Information > USB

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Answer 4

mgs222 Author

Level 1

5 points

Jul 23, 2025 4:50 PM in response to Grant Bennet-Alder

That is strange. It shows enough power. And it shows the two partitions. Yet Disk Utility shows nothing. Any thoughts?

[Edited by Moderator]

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Answer 5

mgs222 Author

Level 1

5 points

Jul 23, 2025 4:37 PM in response to mgs222

Oh, and when I close and reopen Disk Utility it sits there spinning showing Loading Disks.

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Answer 6

mgs222 Author

Level 1

5 points

Jul 23, 2025 5:03 PM in response to mgs222

About 15-20 minutes after I plugged in the disk, the system mounted the disk. The disk showed up on Disk Utility and the system completed a backup. Now I am totally confused.

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