Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.


macrumors regular
Original poster
May 7, 2013
Sydney Australia
Hi, I have two internal and two external drives, I'm trying to format all my drives to APFS My High Sierra drive system is APFS and one of the external drives is APFS the other two are Mac OS Extended system, when I try to convert them I get the following error, The operation couldn't be completed error-69888.
Even trying to force unmount the volume fails.


macrumors Penryn
Feb 20, 2009
My opinion only, but you're probably better off to "leave APFS alone" for the time being.

It seems to be causing much more grief than it's (currently) worth!


macrumors member
Nov 24, 2016
You need to switch the MBR to GPT disk type to be able to succeed. I used under windows, Minitool Partition wizard 10 (Free) to convert an usb 32GB key from MBR to GPT type, and then inserted it under Mac OS and used the Disk Utility to erase it and format it as an APFS encrypted.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.