Time Machine: iMac not recognizing that external drive is plugged in

Question

Time Machine: iMac not recognizing that external drive is plugged in

Hi,

Upon startup, my iMac has not been recognizing that my external HD is plugged into the iMac. This HD is the repository for my Time Machine backups. The workaround has been unplugging the drive and plugging it back in.

iMac: M3 chip

OS: Sequoia 15.3.2

HD: Samsung 1TB, half of it is free space

Connection: USB-C to USB-C, plugged directly into the computer, no adapters

This is an intermittent issue. I've already called Apple Care and they had me reinstall my computer's software. This seemed to work for a while.

Problem has started up again.

This is annoying and I'd appreciate any help that you have to offer.

Thank you!

iMac 24″, macOS 15.3

Posted on Apr 4, 2025 1:15 PM

Reply

Answer 1

rkaufmann87

Level 10

147,132 points

Apr 4, 2025 2:19 PM in response to anonymous-imac-user

This time around buy a high quality External Hard Disk, many experienced users on these forums prefer the OWC Mercury Elite Pro due to it's:

High Quality enclosure means great cooling that translates into a long life.
Ease of use.
Dead simple to replace the internal HD (less than 2 minutes and a simple screwdriver).
Service available from the vendor.
Very Fair Pricing.
Available in capacities from 2-24 TB

Reply

Answer 2

Apr 4, 2025 3:01 PM in response to rkaufmann87

So, this is a housing for a HD that you would buy separately?

I see a USB 3.2 port and I'm wondering what that's for.

I noticed that there's an AC adapter and cable that comes with the unit. I am wondering why you'd have to have an external power source.

Reply

Answer 3

rkaufmann87

Level 10

147,132 points

Apr 4, 2025 1:57 PM in response to anonymous-imac-user

How old is the Time Machine External Hard Disk AND do you use it for anything else besides Time Machine??

Reply

Answer 4

Apr 4, 2025 2:10 PM in response to rkaufmann87

I was afraid someone was going to ask me how old that HD was.

I bought it / started using it in June, 2022.

The HD is used only for Time Machine.

I think I'll get a new HD.

Any other tips, though?

Thank you!

Reply

Answer 5

rkaufmann87

Level 10

147,132 points

Apr 4, 2025 2:48 PM in response to anonymous-imac-user

One of the major advantages of the Mercury Elite Pro’s is the HD itself is replaceable. Many inexpensive EHDs have sealed enclosures so when the HD fails that means you throw the whole thing away.

That is NOT the case with the Mercury Elite Pros, when the HD dies you simply remove it (use a screwdriver to open it) and replace with another HD. This may sound intimidating but it so easy a 6 year old could do it, yeah and even some adults. :-)