The problem of external hard drives connected via USB 3.0 has been around for quite a while. It is a real mess that I think only Apple can fix. Hopefully, they already have fixed it in the new High Sierra macOS, we will have to see. Basically, I have a few USB 3.0 drive enclosures that do not work.
USB 3.0 Disconnect Overview
The USB 3.0 Disconnect problem is wide spread. I have done extensive research on this issue on the Web. I have tried a myriad of potential solutions to absolutely no avail. Thinking that it was the USB 3.0 enclosures fault, I bought a couple of different enclosures and tired them. They all have the disconnect issue. I have tried enclosures that support UASP and some that do not with the same result. I have performed so many different suggested troubleshooting procedures I cannot begin to list them all.
Keep in mind, I am doing all this on my Late 2012 iMac 27”. I suppose there could be an issue with USB 3.0 on this machine, but in my research I noted this was happening on all kinds of Mac configurations.
As of this writing, I have a few observations to make.
First, as far as I can tell, running an older spinning hard drive in one of these USB 3.0 enclosures is trouble free. That has not been other peoples experience based on my research. But, for me, it seems to work OK.
Second, the reason for using a USB 3.0 enclosure with UASP is for running a SSD drive. I feel the need for speed! All of my trouble occurs when running this configuration.
Third, if I run a SSD in a USB 2.0 enclosure there are no problems. However, the SSD speed boost is gone so it kind of defeats the purpose of running a SSD externally.
Having noted all of this over the past couple of months, I decided to run a little test to perhaps determine the future of my USB 3.0 external enclosures. I installed a Crucial MX 300 512GB SSD in an Inateck USB 3.0 enclosure that has UASP capabilities. Here is the drive:
I just left the cover off because I was going to put the drive back into a USB 2.0 enclosure when finished.
With the SSD drive attached to my Late 2012 iMac, I booted into my macOS High Sierra Beta install. Then I proceeded to work in that environment for about 30 minutes. Here is the drive on the Desktop:
The external USB 3.0 drive never disconnected. Now keep in mind, I do not have very much software installed in the Beta, but I was still pretty encouraged by the results. When I booted back into my macOS Sierra install the USB 3.0 external SSD started disconnecting again.
Heck if I know!! It ran fine in High Sierra, but I do not have much software installed in there. So, does High Sierra fix this issue? Or, is everything fine in the current Sierra OS, but one of my software packages is causing this disconnect?
Is there something specific to my iMac hardware that is the problem? I do have several external hard drives attached along with a couple of other USB peripherals. I have done so much testing it is all a blur, but I seem to remember unplugging all externals except the USB 3.0 enclosure and having it still disconnect.
I really do not know what the solution is for this issue. I am hoping against hope that Apple has fixed this in macOS High Sierra, that would be totally awesome. We will just have to wait and see.