The Mojave cannot recognize external hard drive.

well, i had the same experience one day, when my external drives would not show up... via usb cable.. So i looked online and did all that malarky, finder - preferences, sidebar, etc..., app-disk utility-mount...etc.... ( And these elaborate re-boot and check everything strategies almost never solve any Mac problem i've ever had )

Then today i hovered the mouse in the sidebar of the finder window, just to the right of iCloud, and noticed that "hide" would appear with the mouse hover, and of course if you click "hide" the iCloud drive goes away and the hidden link now says "show"... it toggles.... Ok, so just below that, where Locations would be showing my external drives and stuff, the toggled INVISIBLE link was of course hiding everything, so i hovered there, clicked "show" and Voila ! all my externals were back again...

I don't know what made Apple create these INVISIBLE toggles, or what made my computer toggle it off in the first place, maybe a stray mouse click on my part... Anyway, try this, see if it solves the missing externals for you.

I had the same problem with my powered Anker USB3 hub when updating the OS once. I did an SMC and NVRAM reset and it was recognized again. I'm not sure why but it was like the OS had to be forced to "see" the hub again.

An interesting thing to check when this happens:

Click on Apple Menu (top left)

Hold Option and "About this Mac" will change to "System Information..."

Click on "USB" under "Hardware"

There you can see what the Mac is seeing on your USB chain.

Zolablue wrote:

Do you happen to have a Seagate external drive? Seagate is not supporting the latest update to High Sierra either. I found a couple options and I have emailed Seagate. Before I post further let me know if you are using Seagate. We both may be out of luck with new iOS being unsupported.

Are you using the Seagate software that came with the drive? If so then you should uninstall it and, if possible, reformat the drive with Disk Utility. The software that comes with Seagate and WD drives are not needed for Macs to use those drives.

That will entail copying the files to some other drive so the drive of interest can be reformatted.

I went through the same problem here. Wish I had found this thread yesterday. My faithful USB 2.0 powered hub apparently is not good enough for Mojave. Once I removed it (the hub) from the setup and plugged my HDDs directly on the iMac USB ports, everything went back to normal

I too, had this issue- perhaps a little different. I updated to Mojave from El Capitan yesterday. For a very long time (at least 2 years) I have been using a 4 port USB hub (not powered/plugged in to AC) connected to my iMac. Connected to this were three different WD external drives. Everything worked perfectly until I switched the OS.

Went through a reinstall of the Mojave OS. Still had a problem with the hub. External drives plugged directly into the iMac via USB worked fine, but not when using the hub. Installed a new multi-port USB hub (powered), and all is now working.

Nobody with Apple Support could identify the problem or explain why the hub suddenly stopped working when switching the OS.

If using multiple external drives, I suggest checking your hub for power, or switching out the hub. Worked for me.

Have you tried resetting SMC? Solved the problem of not recognizing my external optical drives, at least temporarily. Periodically need to re-do, but drives show up again.

Starting in safe mode, then restarting worked for me! I've tried so many things over the past 4 hours. THANKS!!!

I had this problem with an external optical drive and did the ‘reset the smc’ Trick. My optical drive mounted and let me burn cds. I just plugged in a couple of external HHD drives, they are both currently mounted. For emergencies and specific tasks, I have a micro SD card installed in the SD slot on my 2012 MacBook Pro with Sierra installed, cab boot from that when necessary. A hassle but solves the ‘no longer supported’ problem with newer OS.

How is your drive formatted and connected to your Mac? It should be formatted OS X Extended (journaled) with ownership set to be ignored.

Go to the brand name of the hard drives website and see if they have a tool kit to download an up dated drive for example mine was seagate so I went to this site: https://www.seagate.com/support/software/toolkit/

I had same problem with Mojave not recognising any of my Samsung M3 portable drives, which are all NTFS as need to use Windows too at times. They all came with pre-installed Paragon software. I contacted Paragon and they sent me a link to download an updated version for Mojave. All drives now being recognised and back to normal. Suggest that some of you may like to contact the software manufacturer support for advice. Email for Paragon is support@paragon-software.com

The fix for my problem looked complicated till I read this solution. I switched out my Apple hub for a StarTech and instantly my problem was solved.

I had been trying to hook up a new external HD but kept getting an error message. This solution worked for me and it was simple.

This video helped me to get Mojave to recognize my Seagate hard drive: https://youtu.be/DVgMd4unhTQ

Starting in safe mode, then restarting worked for me!

This also worked for me! My Drive was formatted in Mac OS Extended (Journal)

No, if formatted OS X it can't be used with Windows PC.

It is NTFS

That's why. You had some 3rd party software so you could read and write to it. With the Mojave upgrade that software was removed so it will have to be added again. Make sure to get the latest version

You do know that a Photos or iPhoto library can't be used on a NTFS external hard drive, right. Just a heads up.