External hard drive won't mount in high sierra

Could you explain what you did in more detail, please? What did you search for in Spotlight that you then turned off? Did you reboot before you connected your external HD?

YESSSS!! OMG, thank you. That was what was missing. PHEW!!

You have the answer. I usually have that option on by default and got lazy and forgot about it. I am now able to format my new external.

THIS WORKS! and should be the first answer seen on this questions. I've been banging my head for HOURS!
Thank you!

The same goes for me. Have you found any solution?

that did not work for me...

This is only way finally worked at my Mac after changing with spotlight's setting

thank you very very verymuch,

i have that same issue and how does this problem get solved?

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.

tried doing the same by turning off all results for searchlight...that did not help. I am having trouble mounting 2 Seagate USB drives that are formatted NTFS. They show up in the disk utility app but can't be mounted. Downloaded paragon NTFS software and it can't mount the drives either!!

Maybe this will help some users seeing these strange High Sierra external drive mounting issues. I have an external Seagate that I plug in for Time Machine back ups (named Seagate). If I plug in a flash drive that I use to move files to another Mac occasionally, it does not mount correctly. The icon comes up on the desktop, but the name is incorrectly shown as Seagate - when the Seagate is not even connected anymore. If I try to open with Finder or by double-clicking the icon, it will not open. My solution - I reformatted the flash drive (using disk utility) to use FAT32 formatting. Now the flash drive is properly recognized and mounted when it is inserted. Mac OS engineers need to sort these external drive mounting issues out, as this thread shows a bunch of people having problems.

I tried your solution and it worked! As you said, turned everything off in spotlight search results, then unplugged my external drive and plugged it back in and the disk mounted and was fully accessible. Very strange. Am about to restart the computer to see if it stays that way.

I had this error and as mentioned @abuohp this solves my problem. Go have a look :

English : https://frenchw.net/en/2018/04/13/correct-the-macos-error-snap_metadata_val-obje ct-invalid-extentref_tree_oid-0x0/

French: https://frenchw.net/2018/04/13/corrigez-lerreur-macos-snap_metadata_val-object-i nvalid-extentref_tree_oid-0x0/

Hope this helps

FrenchW