External USB Hard Drive Not Working

Recently, a friend had a problem with an external USB hard drive. The external drives is an SSD that is about 6 months old. The SSD is in a USB 3.0 enclosure. After installing the Catalina Supplemental update, the drive was no longer recognized by his 2019 MacBook Air. I could fix the issue, here is what I did to troubleshoot it.

Hard Drive Fix

When you troubleshoot any issue on a Mac, there are two roads you can take to a fix. One road is software related and the other is hardware related. I did not know which road was causing the problem. Initially, I did a few basic troubleshooting steps.

The first thing I did was to connect the external drive to the Air and Restart the machine which did not fix this issue. Next, with the drive connected, I reset the NVRAM by holding down the Command Key ⌘, Option Key ⌥, the “R” Key and the “P” key immediately after restarting the computer. This procedure resets the NVRAM on the computer.1 Basically, you are resetting the hardware which is supposed to force the machine to recognize any externally connected devices. In this case it did not fix the issue.

I decided to take the external USB drive home to my workstation where I could do more testing. At this point I was not sure if the SSD was failing, the USB 3.0 enclosure was failing or if it was some type of software issue. Here is what the drive looks like:

You slide the bottom or top off and plug in your 2.5” SSD:

But, I digress. When at my workstation, I plugged the drive into my iMac. It did not show up on the Desktop. This eliminated software issues, my machine runs pretty clean. Next, I removed the SSD from the enclosure and installed it in a known good enclosure. The drive showed up immediately on my Desktop. It was looking like the original enclosure was dead, but just to make sure I put another known good SSD drive in it. When I attached the original enclosure to my Mac a different SSD inside, it did not mount on the Desktop. The moral to the story was a dead enclosure.

I use hard drive enclosures all the time. They are very reliable, but they can go bad occasionally. I do not buy expensive enclosures, so I guess you get what you pay for.


When troubleshooting problems between a Mac and an external device, you have to determine if the issue is software or hardware related. The determination will get you on the right path to fixing the problem.

  1. This procedure used to be called “zapping the PRAM”.