#Could not unmount disk when formatting how to#
#Could not unmount disk when formatting install#
#Could not unmount disk when formatting upgrade#
#Could not unmount disk when formatting verification#
#Could not unmount disk when formatting password#

It could also happen if the disk you are trying to erase has failed the process with a Couldn’t unmount disk error. Couldn’t unmount disk: (-69888) error on Mac pops up when the current boot drive is being modified.

#Could not unmount disk when formatting how to#

There is usually very little to no additional details given as to how to fix the problem or even what the problem is about, making it harder for users to understand this issue.īasically, the “Erase process has failed.

#Could not unmount disk when formatting verification#

This issue can pop up when doing partitioning, disk verification and repair, or even during formatting. Couldn’t unmount disk: (-69888) error on Mac can stop whatever task the utility is attempting right in its tracks. But sometimes a frustrating “Erase process has failed.

If it happens while you were trying to do an upgrade, you might need to do these steps inside a virtual machine or a working hackintosh.Disk Utility usually runs trouble-free most of the time.

#Could not unmount disk when formatting upgrade#

You should probably not directly upgrade from El Capitan to avoid this problem. You might of course not need to create two partitions in this case. This should also work for Chameleon bootloader. Reboot from the USB drive and everything should go smooth and without this error.

#Could not unmount disk when formatting install#

Install Clover to the first partition of your USB drive named CLOVER (unless named otherwise).You need to typically copy the following files: AppleDiagnostics.chunklist, AppleDiagnostics.dmg, BaseSystem.chunklist, BaseSystem.dmg The same way, copy the other files from OS X Install ESD drive to the root of your USB (the root, not inside a folder on the USB drive).Copy ' Packages' folder from there and paste it in your USB/System/Installation. That's actually an allias (or a shortcut if you want). Inside the USB drive, go to ' System' then ' Installation' remove the file named ' Packages'.Open the USB drive (the name ' USB' will become ' OS X Base System', that's why you need to smartly unmount the other one using Disk Utility to avoid confusion.).Upon finition, smartly unmount OS X Base System disk under ' Disk Images' in Disk Utility.If so, type it in and click ok then wait.

#Could not unmount disk when formatting password#

You might need your password to complete this task. You should see ' Restore from: OS X Install ESD' click on ' OS X Install ESD' and choose ' OS X Base System' from the dropdown menu. On the status bar, click on ' Edit' and choose ' Restore'.

While still inside Disk Utility app, click the second partition (it's should be named USB).

It's needless to say that you should backup its contents first. Of course, everything on that drive will be destroyed. The second one's format should be OS X Extended (journaled) and give it USB as name. The 200MB partition format should be MS-DOS (FAT) and give it CLOVER as name. One with 200MB and the other one with whatever size you want. Click 'Partition' and create too partitions. Right click on BaseSystem.dmg and click open to mount it. Make sure that hidden files visible (there are many ways, use Google). If so, then right click on the file, click 'Show Contents Packages'.

I assume that you have downloaded the installation from Mac App Store.

Use the 'Restore BaseSystem.dmg' method to create the installation USB.

RecoveryHD = El Capitan recovery drive.

Macintosh HD = El Capitan drive (already installed and working).

Sierra = New partition created for Sierra.

MSR = Microsoft Reserved (culprit, too?).

It could have been due to that, although MSR partition is also known to cause problems in some situations. In my case, I used MiniTools Partition Manager to migrate my Windows installation from my HDD to the new SSD drive. The root problem probably has much to do with the partitions structure.

The problem is that it for some reasons tries to unmount the partition it has booted from, which is obviously not possible hence, it fails. First, it copies the installation files to the HDD partition (that part creates problem), and then it reboots from that partition to install the files and eventually create the Recovery partition. If the USB is in fact created with that tool, the installer divides the installation process into two. The problem I believe was due to the createinstallmedia tool. Then, I thought it was the fact that I was using the installer in El Capitan to install it to the new partition. At the first, I thought the volume was dirty, so I booted to my working El Capitan again and had formatted the partition again. It always ended up with a NASTY error message saying that it could not unmount the volume for repair (what repair, anyway?). Recently, I have been having weird issues installing Sierra to my newly created partition.