Unlocatable partition on MacBook Pro mid 2015

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Level 1

4 points

Unlocatable partition on MacBook Pro mid 2015

I recently upgraded to Catalina to do some development work in most current Xcode/Swift, only to discover MS Office software doesn't work, as well as a bunch of other annoyances. I rolled back to El Capitan from Time Machine and all went well, except my Windows 10 on Boot Camp some how got deleted. I went through the Boot Camp process only to have it fail due to the > 5Gb file size issue (Win 10 originally installed when it was smaller!). After trying a multitude of methods to re instate Boot Camp, I've ended up with my 256 Gb SSD now totally occupied by the Macintosh HD, even though it has retained only the 162 GB I allocated it - the other 90-odd GB (allocated to Win10 in the Boot Camp disaster) nowhere to be seen.

Ive tried using Disk Utility to wipe the entire disk bare, but it only identifies the 162GB, despite there clearly being 250+ Gb.

I've not found any methods, standard or otherwise, to achieve this. Does anyone have any suggestions/solutions? Any help much appreciated.

MacBook Pro 15", OS X 10.11

Posted on Nov 4, 2019 2:55 PM

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Answer 1

Top-ranking reply

HWTech

Level 9

60,302 points

Nov 4, 2019 5:53 PM in response to Lazamac

Whenever macOS gets this way I just write zeroes to the beginning of the drive to overwrite the partition table after which macOS usually will usually be able to partition the whole 250GB drive. I don't know if this can be accomplished from local recovery mode, but it definitely can be done from Internet Recovery Mode, or a macOS USB installer, or possibly a bootable TM backup.

I believe the internal SSD will be identified as "disk0" (that is a zero) regardless of what media you boot from, but it is always a good idea to double-check before writing zeroes to a drive. The safest option is to boot into Internet Recovery Mode so you do not risk destroying your backup.

Verify the drive identifier for the internal Apple SSD:

diskutil  list  internal

I do not know if the "internal" option is available with El Capitan, so if the previous command doesn't work, then use the following option, but you will have to search through a lot of items to find it in the list:

diskutil  list

You may need to unmount the "Macintosh HD" volume first (assuming the volume is still named "Macintosh HD"):

diskutil  unmount  "/Volumes/Macintosh HD"

Then use the following command to zero out the beginning of the drive. Make sure to replace the "disk0" with the correct drive identifier for your internal Apple SSD:

sudo  dd  if=/dev/zero  of=/dev/disk0  bs=100m  count=10

Once this finishes, try using Disk Utility to erase the drive again. Hopefully you will now have a 250GB volume.

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Answer 2

Lazamac Author

Level 1

4 points

Nov 4, 2019 10:24 PM in response to Grant Bennet-Alder

Thanks for getting back to me. I had already tried the 'diskutil list' to no avail, it showed nothing new. Here's the screenshot I just took re-running it:

I'll try the 'zero-out' suggestion and let you know the outcome. Many thanks!

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Answer 3

Nov 4, 2019 8:16 PM in response to Lazamac

That just shows Mounted partitions.

Try the Partition Icon and post that screenshot, or type in Terminal:

diskutil list

to see a list of all partitions and what real and virtual drives they are assigned to.

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Answer 4

Lazamac Author

Level 1

4 points

Nov 4, 2019 10:27 PM in response to HWTech

Thanks for getting back to me on this so quickly. The DISKUTIL LIST I had performed quite early on; it revealed nothing. I'll try the 'zero-out the beginning of the drive' and get back to you. Many thanks for your help.

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Answer 5

Nov 6, 2019 5:53 PM in response to Lazamac

Based on that, one possible guess is that the Disk Utility in El captain could not deal with the drive modified by Catalina.

The Utilities and the MacOS Base System used for a new Install are always the newest version for that MacOS, so a bootable USB stick for Catalina contains the latest Catalina version of Disk Utility.

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Answer 6

Lazamac Author

Level 1

4 points

Nov 6, 2019 10:26 PM in response to Grant Bennet-Alder

I created a bootable El Capitan USB from a legacy copy of El Capitan on a Macworld source site, as I wanted a clean El Capitan system to re establish Boot Camp on. Possibly my Time Machine back up of EC that I restored from after the Catalina upgrade had a corrupted Disk Utility, but your point is well taken: variations from one OS version to another may not be apparent until some problem befalls your installation, and a remedy may not be apparent. The key lesson is to have robust back ups from which to restore. Once again, thanks for your insight and assistance. I’ve learnt so much from this episode that I would not have otherwise, so there’s a positive in it after all.

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Answer 7

Lazamac Author

Level 1

4 points

Nov 6, 2019 5:35 PM in response to Lazamac

After creating a bootable USB drive, I was able to use Disk Utility in the Restore process to erase and re-partition the whole SSD back to 250 Gb. Thanks to you both for your assistance.

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Answer 8

Nov 7, 2019 7:32 AM in response to Lazamac

<<The key lesson is to have robust back ups from which to restore. >>

Amen to that!

Glad you got it sorted out.

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