External hard drive not visable with 2023 24-in iMac running Seqoia 15.5

Have you tried rebooting the computer?

Disconnect all other external drives, then run the following command in the Terminal and post the output here:

diskutil  list  external

texaskellys wrote:

Not sure what you mean by output as I never use and not real familiar with the Terminal App. All I can tell you is I entered the command you provided and hit 'ENTER', but nothing happened.

If nothing appeared on the screen including no error messages, then it means the physical drive is not seen.

This could be an issue with the USB port, the USB cable, any adapter/dock/hub that is being used with it, or it may mean the physical drive itself is dead or not able to communicate. If you are using good quality cables/adapters and the issue occurs when the drive is connected directly to the Mac and also when using a USB hub, then the drive itself is most likely at fault.

Do you have another computer you can try? It can even be a Windows computer. As long as you don't erase the drive or initialize the drive, then the data would not be touched. You would need to launch the Disk Management app on Windows to be able to see whether the physical drive is shown since the file system on the drive may not be recognized by Windows within File Explorerer.

texaskellys wrote:

When connected through USB to an HP, the drive shows up under disk drives in device management but not listed in explorer. Device management says the device is working properly. It is not listed in disk management.

Then the physical drive is working & communicating which it apparently was not doing with your Mac. So the issue is with your Mac and/or anything cables/adapters needed to access the drive compared to accessing it from Windows.

Ok, the WD MyBook was indeed my backup operating with Time Machine on my Mac. Can you please tell me what would have to be installed on my wife’s HP laptop in order to read the MyBook folders and files I have backed up there?

That was critical information to know since TM backup drives are not quite the same as a standard data only drive.

While there is a paid third party Windows driver available from Paragon to access an APFS volume, I would be very careful since you do not want it to make any modifications to the APFS volume.....especially a TM backup drive. Unfortunately the default when connecting drives is usually to allow writing.

TM uses special linking to get be able to show the history of every file in the backup and requires the use of the TM backup software within macOS. You may be able to access some files manually, but I don't know what you may be accessing.

in the Finder select Computer from the Go menu. does it appear there? If it does drag it into the Sidebar in the Favorites section.

texaskellys wrote:

Does not show in Disk utility.

What is the format of the drive? If you plugged it on and installed the bundled software and did not format it for use on a Mac, then the bundled software may be incompatible with this version of macOS and it is preventing mounting of the drive.

How is the drive powered? Does it get power from the USB port or does it have its own power? If bus-powered, it may be trying to draw too much current.

texaskellys wrote:

OK, the Apple server finally connected and I got my computer back on. Immediately entered the command you sent me in Terminal after disconnecting MyBook and an external CD drive, re-connected and still nothing showing in Finder, even after opening a new Finder window.

What was the output of the command? It was meant to tell us whether the physical drive was being seen. If the physical drive is not seen, then that is one problem. If it is seen, then that is a different problem most likely related to the file system or possibly a faulty drive itself.

texaskellys wrote:

UPDATE: I was able to see the MyBook when hooked up to my wife's HP laptop. so that ruled out a bad power or USB cord. So I purchased the Mac Toolbox from Paragon which allowed me read what was on the MyBook. I copied the last full backup from the MyBook to a brand new SSK dual USB/USB-c thumb drive,

Did you see your files when you used Windows File Explorer to navigate that drive? The Apple alias & links may not be recognized by Windows or the Paragon software. I know the Windows' shortcuts don't always translate correctly when viewed from another OS.

plugged it into the same Thunderbolt port on my "Renewed" 2023 24-inch iMac, which now appears in my Finder sidebar just like the MyBook used to, so that tells me there is nothing wrong with the port.

Not always true, but the port is probably Ok.

I found the latest backup file there but the problem now is I don't know what to do with it because it looks nothing like it did when viewing the MyBook through Finder, before that mysteriously disappeared. I naively thought I would see my folders just as they appeared in the Finder sidebar.

You must have missed my mention of a TM backup drive having special customized links:

External hard drive not visable with 2023… - Apple Community

"TM uses special linking to get be able to show the history of every file in the backup and requires the use of the TM backup software within macOS. You may be able to access some files manually, but I don't know what you may be accessing."

Sorry, I know that's a lot to digest, and it's all Greek to me. Will any of that get my folders and files back from my Model MRQY2LL/A 27-in iMac if I schedule an appointment at the closest Genius Bar?

Unless an Apple tech is able to magically mount your TM backup drive, then I don't think the Genius Bar will be able to assist you.

Without the external TM backup drive connected, launch the TM app to see whether you may have any local TM backup snapshots on your boot drive.

texaskellys wrote:

When I launch TM without the MyBook connected I get a setup popup saying, "You haven’t selected a location for Time Machine backups."

If you were using TM for backups on this computer, then this computer should have some APFS TM snapshots. You can try manually checking for APFS snapshots just in case there is more going on here by using the information in the following Apple article:

View APFS snapshots in Disk Utility on Mac - Apple Support

NOTE: You must first click on the "Data" volume on the left pane of Disk Utility before the option to "View APFS Snapshot....." is made available to you, unfortunately Apple omits that very important part from their documentation. If there are APFS snapshots, then you can mount one & navigate it within the Finder to see if it contains your data. The oldest snapshot is the most likely one to contain the data since the others will generally be replaced until a TM external drive is connected.

texaskellys wrote:

BTW, Favorites is missing from the sidebar as well

Is the header completely missing or is the disclosure triangle just turned to hide the contents?

Open Activity Monitor>Show all processes, look to see if fsck is running?

Does it show in disk utility?

texaskellys wrote:

Was that procedure you linked for viewing APFS Snapshots supposed to be initiated on my original iMac in order to find missing data and files?

It is meant for whatever computer which had those documents & the TM backup that will no longer connect/mount.

Same thing regarding my previous suggestion to launch the Time Machine app to see if any local backups are present on the boot drive.

These are just two long shots since the only other option would be to have someone actually physically examine your TM backup drive (MyBook) who knows something about macOS troubleshooting, TM, and data recovery to see if there is any way to get access to the items on the TM backup drive (MyBook).

Just like there is NTFS software that allows a Mac to write to NTFS (windows file system), there is software for a PC that allows you to read/write APFS (Apple File System). While a Mac can read NTFS, Windows cannot read any Mac drive format without installing software. I don’t know specifically, but I think the same people make them, Paragon definitely and maybe Tuxera.

Since the drive came pre-formatted, it may be in Mac OS Extended format. Paragon has software for that and I don’t know if they just have one that handles both.

is there a way to get the MyBook back in my Finder sidebar and not have to buy anything?

No idea at this point. Can’t tell what is wrong. I thought you were just hooking it up to a windows PC to see if it works. You wouldn’t be able to do that without something on your HP that can read any Mac formatted drive. Windows can’t do that out of the box. If you can find another Mac, that would be a better idea.