I upgraded from El Capitan to Sierra on my iMac, now it no longer recognizes my external USB hard drive. Not cool. Easy fix or big problem?
iMac with Retina 5K display, OS X El Capitan (10.11.2)
How is the EHD formatted?
Verify that the Finder preferences are set to show external HDs:
If it is, toggle it on and off a couple of times, reboot if necessary.
Next, boot into Safe Mode, Mac OS X: Starting up in Safe Mode, and see if it shows there. Reboot normally and check again.
Download and run Etrecheck. Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.
Is it recognized on another computer? If not - it's your external hard drive that's the issue and not the computer/OS.
If it is seen on another computer, if you open Disk Utility on your Mac, does it show the external HDD there? If so, it's possible that you don't have it enabled in Finder Preferences to be seen. If you do, you can reformat the external HDD (in Disk utility by choosing the "Erase" tab), if you only use it with Mac OS you want to format it as "Mac OS Extended (Journaled) OR if you use it with both Windows and OS X you want to likely format is as Ex Fat (file size limit is larger). Keep in mind, if you use it for Time Machine back ups, it needs to be formatted for Mac OS Extended (Journaled) - if you use it for both you can create a separate partition for both.
If it's not in Disk Utility, you can try resetting SMC Reset the System Management Controller (SMC) on your Mac - Apple Support to see if it fixes your issue.
If not, you want to look at purchasing another external HDD.
I can't see my external usb hard drive after installing Sierra. Not cool. Thoughts?
