External hard drive won't mount in high sierra

I don't believe it has anything to do with USB. It doesn't work for me when using both USB and Thunderbolt. After some digging, I think it all has to do with High Sierra and APFS. High Sierra is deemed one of the worst OSX updates in Apple's history and it could be simply just a lack of support for spinning HDD drives and that's why nothing will mount. Unfortunately, that makes this a waiting game for an update to fix all of this due to Apple leaving HFS+ and going to APFS.

HS has about turned a 10 + year Mac user against them. I have lost so much time and money it's pitiful. If they don't get their junk together I will be selling a Macbook Pro, 27" iMac, iPad Pro and 2 new iPhone 8s and going to PC and android. Ever since Steve Jobs passed the company is going to the dogs. Get your act together Apple!

I cannot believe this is happening AGAIN. Several years ago, I installed an OS update and Time Machine no longer worked with external drives. I contacted Apple via phone and of course, no one knew anything about the problem. After spending hours trying to figure out what was wrong (they tried various steps with me) including taking the machine and drives to the Genius Bar, to no avail, it turned out that the update was the problem and eventually a fix was offered in another update.

So, this time, I waited a LONG time to install High Sierra (today), thinking that the major problems would have been resolved. But I am having the same problems you described, with two drives, although one is recognized but backs up VERY slowly. As I read the replies this problem was introduced with a mid-Dec. update. So even waiting a long time doesn't help! Come on, Apple, this falls well below your standards--and to have it happen twice, is really bad.

Had similar issue. Open disk utilities. If none of these drives show up look for the menu (new in High Sierra) that states "show all". If drive shows up try repair and if that does not work you may need to reformat it if nothing on that needs saving. I had two drives that I needed to fix that way. They were both fine with Sierra but High Sierra must be doing something different.

I have the same problem. I have the very newest MacBook Pro, my WD External hard drives won't mount. In Disk Utilities, the drives are visible, however, "first aid" is unsuccessful and they won't reformat either. In my case, the lights on the external drive flash, and you can hear the internal discs spinning normally.

My Toshiba Canvio is connected in System Information but doesn't mount. All of my research so far seems to agree it is due to the files system change. I always wonder what will stop when I accept these updates. Hope a fix emerges soon.

THANK YOU!! I did this and checked the box that said "Show ALL Devices". Sure enough, I was able to reformat my brand new WD External Hard Drive and now I can read and write to it. Thought I was screwed by High Sierra. No more OS updates for me. Maybe.

When you are in DU, look in upper left corner an there should be a View option. click on that and you should get an option to Show All Devices. THAT was the key for me as DU then recognized my new external hd and I was able to format and partition it as I wanted.

When you are in DU, look in upper left corner an there should be a View option. click on that and you should get an option to Show All Devices. THAT was the key for me as DU then recognized my new external hd and I was able to format and partition it as I wanted.

Me. You create update that makes previous external disks unusable, and when people complain you poke fun at them? There should be a RED big warning that you are changing underlining filing system that will not be compatible with previous hardware.

vilko wrote:

Me. You create update that makes previous external disks unusable, and when people complain you poke fun at them? There should be a RED big warning that you are changing underlining filing system that will not be compatible with previous hardware.

External disks are not made unusable. You have a configuration or procedural problem. If you want assistance please start your own thread providing your system details and the details of your issue.

I guess waiting for an update makes the most sense?? I have a WD My Passport Ultra that is not recognized. I can see it in Disc Utility but it will not "mount". I noticed that the last High Sierra update was in mid December, which was when this hard drive (which I use for Time Machine), stopped working. Haven't had a backup since then. Ugghh.

Thank you for your insightful post. This is frustrating. I hope that Apple puts a fix in the next update because it seems that this issue is prevalent.

Many thanks. I solved the problem first by going back to my old MacBook Pro with an old version of OSX. In DU it showed all parts of the drive (by default) and not just the volumes. While it was being fixed I read your post so hence I have switched to "show all devices" on our other Macs.