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macrumors newbie
Original poster
Nov 27, 2017
I'm running El Capitan and decided to install High Sierra on a clean partition.
After installing Sierra and booting from the Sierra partition, I rebooted from the El Capitan partition and decided I wanted to erase the High Sierra partition.

Now when I open Disk Utility in El Capitan the partition High Sierra is installed on doesn't show, nor does after rebooting.

It's an SSD drive.

In the pie chart I do get it, but when I try do delete it it says, couldn't read partition map.

Any help or ideas?
Last edited:

Bart Kela

Oct 12, 2016
Since you didn't bother to post a photo of the Disk Utility screen(s), it's hard to say what happened, but I'm guessing that the High Sierra installation converted that partition to APFS and left the other partition(s) as HFS+. Previous versions of macOS are unable to read APFS volumes.

My suggestion would be to create a bootable High Sierra USB thumb drive, boot off of that and reformat the High Sierra partition as HFS+. Don't install anything, just shut it down. Then boot from your El Capitan or Sierra partition.

This is one example of why I don't create multiple partitions on the same physical disk. It's far simpler to plug in an external drive and install whatever you want on the target drive. Managing multiple boot partitions on the same drive is usually a big headache.

I learned this diddling with Windows and Linux on a homemade PC and mucking around with LILO and GRUB. Ultimately, it was far easier getting a drive bay with removable drive sleds rather than managing boot options in software. That was circa 2000.


macrumors Penryn
Feb 20, 2009
If you want to experiment with High Sierra, I'd recommend that you install it on an EXTERNAL drive, and NOT on an internal partition (with El Cap on another).

I just think the install will go better that way.
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