Time Machine Hard Drive Unmounted

I have an external HD partitioned into two parts: File Storage (used for cold storage) and Time Machine. The Time Machine partition is now showing as Unmounted in Disk Utility. I believe this may have been caused as I had it plugged into my USB-C monitor, however, when the monitor goes to sleep I’m guessing this kills power to the drive and causes an issue. This is a bit of a pain as it’s half the reason I chose to get a USB-C monitor (to use it as a hub). Anyway… Now that the drive is unmounted, can I get back my Time Machine backup? Or is it all gone?

Sounds like your backup should be OK.

In Disk Utility
Right Click on your Time Machine Volume
Click on Mount

Thanks for the response. When I try that I get the following error:

CleanShot 2020-04-07 at 16.42.20

Test the drive with disk utility

1 Like

com.apple.DiskManagement.disenter error 0 - Not the simple problem I expected.

I found several discussions of this and similar errors from users running Catalina. Let’s see what others may suggest. I’m going to do some more research.


If you’re on Catalina:
I think the error is because the system is waiting for a disk integrity check to finish
(Catalina runs a hard drive scan when it was removed improperly)

What happens if you wait half an hour or 3/4 hour?

When your monitor cuts of power your disk will not unmount cleanly and the disk needs to be checked.

I would recommend not having time machine disks unmount in this way, because you’ll probably get backup integrity errors faster this way. The consequence of which is that it will have to re-do the backup fully. This defeats the purpose of having a TM backup, and you would be better off cloning your disk weekly with CCC or similar software.

If not:
I have no idea.

Thanks @JKoopmans I waited and this didn’t help. It’s looking more and more like I’m going to have to erase the drive and start fresh.

It is unfortunate that part of the value of using a USB-C monitor is to use it as a hub but then I have to plug the drive directly into my Mac to avoid issues like this.

Maybe set the monitor to not sleep or to go blank after some period. On my iMac I have the display set to sleep but never for the computer.

Just for the record, I’ve never had this problem with the LG monitor Apple sells, and I admit it’s a very nice way to keep the Time Machine drive connected regularly with a laptop.

Perhaps there’s a setting somewhere in software that can be changed? I know that several years ago I had a problem with this LG monitor that required me downloading LG’s crappy software to fix. (By “crappy” I mean that it is confusing and ugly, not that it doesn’t work.) Up until then the monitor worked fine so I had no idea that this was even an option.

I wonder if an independently-powered hub connected to the monitor would fix the problem? The hub would have to supply enough power to keep the drive happy, but these are available (OWC makes a few).

The monitor does not have the option to keep the power on that port on?