OS X stopped auto mounting external drivers

hard drivemojavemount

My MacBook stopped auto-mounting external hard drives this week. I have to mount them in Disk Utility, which works fine.

This has happened with three different drives (which all had Time Machine volumes). Flash drives still auto-mount, as did an SSD.

I think this may or may not have coincided with installing Parallels Desktop, but I haven't been running it, even in the background.

This is a 2016 USB-C MacBook Pro running 10.14.4.

Best Answer

Encrypted Core Storage and macOS 10.14.4

macOS 10.14.4 changed the behaviour of auto-mounting Core Storage/HFS+ formatted encrypted drives. These drives appear to no longer be automatically mounted.

Please let Apple know this change of behaviour in a minor macOS update is causing you problems. The more people who provide feedback, the better and the better the chance of it being assigned engineering time.

See Automatically Mount Encrypted Core Storage Volume (10.14.4+).

Related Solutions

MacBook – How to keep the Recovery HD and EFI partitions from automatically mounting on the MacBook Air

Your computer is currently set to mount and show hidden partitions, which is unusual. To get control of this feature, you need to activate the Debug menu in Disk Utility which then gives you the option of viewing and mounting hidden partitions, or indeed, making them hidden again.

In Terminal, run the command

defaults write com.apple.DiskUtility DUDebugMenuEnabled 1

Launch (or relaunch Disk Utility)
In the Debug menu, uncheck Show Every Partition.

SMB: auto-unmount then unable to re-mount without restart

I'm going to put up an answer to question 3. Not sure the rest can be easily diagnosed.

"If an auto-unmount occurs, how can I re-mount the directory without restarting?"

Try diskutil umount /Volumes/josh and it should do the trick.

The "File exists" error is showing up because the mount point it wants to use is already present. Looks like the disk isn't actually unmounted, just that Finder can't see it. This is why Matlab can still access the files on it.

Best Answer

Encrypted Core Storage and macOS 10.14.4

Related Solutions

MacBook – How to keep the Recovery HD and EFI partitions from automatically mounting on the MacBook Air

SMB: auto-unmount then unable to re-mount without restart

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