External hard drive not mounting Mac

After hours and hours of research and testing I solved this for me.

When I plugged in my external hard drive it showed up in my drive in Disk Utility but it was grayed out.

I could not mount my hard drives and it would not let me repair, erase, nor partition them, an old and a new one.

I decided to click on the view button at the top right corner of my disk utility app and I had "Show Only Volumes" selected. So I clicked on "Show All Devices" and this showed me each device the volumes were on. I could now select my external hard drive and I was able to easily repair, erase, and partition my hard drives when I clicked on the device instead of just the volume.

I hope this helps anyone.

camd wrote:

Thanks. This is the information relevant to my situation:

Devices formatted as Mac OS Extended (HFS+) can be read from and written to by devices formatted as APFS.

Unfortunately, either the information from Apple is inaccurate, or there is a different problem with my hard drive and/or High Sierra because my HFS+ drive cannot be read from my APFS device.

Exactly.

I have the same problem with 3 of my 4 external drives.

I can access them in Terminal (/Volumes/), but they are not appearing in Finder.

If I use the common "open <drive's name>" I can access the contents, but the drives' names get mixed up.

Also Lightroom finds the drives, but also mixes up their names

APFS on your boot drive has nothing to do with it, your old HFS+ drives should work. That said, the most common reason for disks not mounting is that they are damaged. You can try repairing the disks using Disk Utility or DiskWarrior.

I have had this problem since the El Capitan (sp?) OS, where I could mount my WD USP hard drive but it would not eject properly and then was no longer "seen". With each new OS upgrade I have tracked the problem on forums, and now, with High Sierra it will not even mount!! I have had it!!! My thumb drives DO mount, and I bought a WD MyCloud WiFi drive for my Mac Time Machine. *** is with Apple????

I've just had this same issue.

I updated to High Sierra a couple of days ago and a 500GB external drive that was fine a few days ago suddenly wouldn't mount today.

I tried it in a Win10 machine while I was searching and found this forum post (it's FAT formatted) and the drive was fine, so after reading the replies here, I restarted my MacBook Pro and tried again and it came up immediately.

I have no idea why it happened or how it is now "fixed".

Thank you, CountJohn. My WD 1.5 TB USB is sitting on my Mac desk shelf. It has been replaced

By a new WD Cloud WiFi drive, and several smaller thumb drives (which DO mount). Apple will

eventually HAVE to fix this! Too many ****** off Mac users!!

- Steven Sunday (can’t remember my nick name)

Sent from my iPad

Same thing. Two perfectly fine external HD's now unmountable, even in terminal using disk utility. Won't reformat as won't mount.

APFS seems to render them unreadable by any Mac. I have tried on Macs running Sierra and no luck.

I copied all my data from the external drive to the Mac upgraded to a clean installation of HS. Then set the new Mac to restore back to the external drive using CCC. Halfway through the backup it failed - and now can't be read by anything.

I plugged second working external drive (Mac-extended), and it won't show up. And now won't show up on any other Mac either.

Anyone got any fixes for this as I don't want to bin two perfectly good external drives.

I just solved the problem Just bought 2 brand new 8TB my books. all failed on High Sierra I have 2 I macs the other was on older software I took the 8TB drives and erased the drives using EXFAT as the option They erased. did it again an set them to MSC OS extended Journeled. Moved it back to the High Sierra machine now and all is good..It appears it is a disk utility problem and for formating and eraseing.. Now running time machine on both...

1TB WD external HD Still won't format!

Hi there

Thanks for this. I can get it to format as EXFAT, but after that when I run format as HFS+ in Disk utility it fails. The message is

newfs_hfs: write (sector 124356): Invalid Argument

File sytem formatting failed

I have tried 5 or 6 times. No difference.

I think this WD passport HD is ready for the graveyard. Not worth spending another day on it!

I feel the High Sierra APFS upgrade is not 100% stable with external HD's judging by how many people have had a similar problem. And no word of warning from Apple on installation process.

Any other ideas for a fix?

I'm having the same problem. I thought my external HDD had died, so I bought a new one; but even with the new one, when I plug it in it won't mount. The annoying part is that any thumb drive does mount when plugged in.

I bought new hardrives to and found all 3 of my Apple computers could not see them. I downloaded "Paragon NTFS for Mac 15" and that saw them immediately and in the program it's easy to format a drive or repair it. Seems Apple have overlooked some basics in their quest to sell more gear without the quality control they once were renowned for.