External Hard Drive Disappeared from Mac Finder

I have a 27-inch 2017 iMac, (Intel silicon), and permanently plugged into it, as my Time Machine backup disk, has been a 5TB LaCie Mobile Drive External Hard Drive with USB-C USB 3.0, which I bought direct from the Apple Store online.


It has been working fine, but this afternoon I woke up my iMac and there was a notification that was 'telling me off' for not ejecting a drive correctly. I had not ejected a drive, nor had I tried to.


But I now found that the Lacie external drive had effectively disappeared from my iMac, even though it is connected by USB-C and there is a steady white light on it.


I have tried unplugging it and plugging it back in; I have tried restarting my iMac. But the drive remains invisible on my iMac. When I open Time Machine settings the drive is listed as being my Time Machine drive, but it says that the next backup will be "After disk is connected", implying of course that it is not connected.


Because it doesn't appear in Finder or in Disk Utility I am struggling to work out how to get it back up and running again. Does anyone have any ideas, please?


iMac is running macOS 15.0.1

iMac 27″, macOS 15.0

Posted on Oct 17, 2024 8:31 AM

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Oct 17, 2024 1:18 PM in response to Tesserax

Hi. Thanks for that.


Right, well the drive does not appear in System Information on my iMac at all.


I plugged it into another Mac as suggested, and it immediately threw up a 'Allow device to connect?' dialogue box. This looked promising so I okayed it, expecting to see the drive appear on my desktop, but it didn't.


There was no sign of it in Finder on the other Mac either, and no sign of it in System Information on there either.


But on the other Mac it DID appear in Disk Utility (see screen-shot), although it didn't look right to me. The bar showing space allocation was all blue and completely full.


The 'Eject' button on Disk Utility didn't eject the drive either, and when I just unplugged it regardless a flag came up saying that D.U. failed to eject the drive 'because it is currently in use', despite being physically disconnected.


So I am still mystified as to what is occurring...


I do now remember that another message did -very briefly- appear on the iMac at some stage, and it referred to a USB device that was using too much power or something, and told me to disconnect it. I can only assume it was referring to the drive, because that was the only thing plugged into the iMac. The drive was already 'missing' from my desktop then though, so I just physically unplugged it.


I am beginning to suspect that the drive is faulty, but it was working fine yesterday.

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Oct 17, 2024 10:44 AM in response to Steve Zodiac

Does it appear in System Information > Hardware, then either under Thunderbolt or USB, depending on how it is connected to your Mac? If not, then macOS does not recognize it and why it's not showing up in either the Finder or the Disk Utility.


Should that be the case, have you tried connecting it to another Mac to see if it appears there?

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Oct 18, 2024 12:57 AM in response to Tesserax

Thanks again.


I think I've hit the brick wall here, though...


When I reconnected the drive to the other Mac it no longer appeared in Disk Utility. Just nothing at all.


The white light is still lit on the drive when it is plugged into anything, but it seems to be dead otherwise.

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Oct 18, 2024 8:41 AM in response to Steve Zodiac

I'm having the same experience. I have a 27" Retina 5k 2017 (Intel) iMac with i5 chip. I have three (3) external drives. One is my TimeMachine, and the other two are redundant backups for video/photo work. I've been fighting with all three drives to mount. MacOS 13.7.


Even when one mounts, after the computer sleeps and wakes up, the drive will no longer display any data or files when I open it. When I attempt to use Disk Utility, it fails b/c "the drive cannot be unmounted." I have to reboot (which takes forever) to get the external drive to mount correctly.


I unplug and re-plug the drives in. I plug them in directly and through a USB 3.0 hub. I power cycle everything. I run them through Disk Utility First Aid (when they mount). Each drive successfully mounts on my work Windows machine just fine.


Time for a new computer? Is there a way to test the input ports?

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Oct 22, 2024 9:58 AM in response to Steve Zodiac

I turned off my Mac Studio computer for 10 days while I was gone. It has 2 external hard drives attached, one for photos/video and one for Time Machine backup. Since I returned, the photos/video drive will not mount. The light is on. I turned it off and on, restarted computer. It doesn't show up in Disk Utility. I don't have another computer to test it on. It was working the day I left. Now it's gone!!! The other drive is fine.

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External Hard Drive Disappeared from Mac Finder

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