Cannot erase Mac Pro partition in Disk Utility on High Sierra

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Level 1

29 points

Cannot erase Mac Pro partition in Disk Utility on High Sierra

I have a 2009 Mac Pro and have 10.13.6. I have the HD portioned into to 2 osX boot partitions. I am trying to erase 1 of them since I don't use it any longer to create disk space. Since this is High Sierra....both partitions, I am not finding a lot of info and am fighting AI to get info.

I want to erase the H2 partition. I am currently in the Nelson "###" partition and I would think I would be allowed to erase the H2. Here is a screenshot of my disk utility. Erase, Restore an Unmount is grayed out. When I select the "Nelson or container disk4" I have the option of erasing the partition.

Do I have this backwards? Do I need to be booted in the H2 partition to erase H2? I don't want to do this yet in case I screw up the whole thing. Or do I have to do a complete reformat of the whole drove and start over?

Earlier Mac models

Posted on Sep 22, 2026 7:15 AM

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Answer 1

Sep 22, 2026 7:35 AM in response to nelsonmay

@MartinR is correct.

I never recommend anyone making multiple partitions on any drive because people almost always find out later that at least one of them is too small and to fix the problem usually requires erasing the entire drive & starting over.

FYI, if you are going to be using the APFS file system, then instead of creating multiple partitions, people should instead create multiple APFS volumes which act a lot like partitions, but do not require creating hard segments & sizes on the drive. All APFS volumes within a single Container share the same storage pool and can be mounted & unmounted independently like a partition, plus they can also be encrypted independently. APFS volumes can be deleted as easily as they are created.

See the following Apple article for details about APFS volumes:

Add, delete, or erase APFS volumes in Disk Utility on Mac - Apple Support

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Answer 2

MartinR

Level 7

26,778 points

Sep 22, 2026 7:43 AM in response to nelsonmay

Unclear if you want to repartition or just erase/reformat, so I'll cover both ...

First, you appear to have 2 physical drives, both Kingston SA400S... drives. Each is partitioned into 2 partitions. Is this correct?

To repartition the disk (KINGSTON SA400S that has Container disk5 (H2) & Container disk4 (Nelson)) you must select that Kingston device not one of its Containers. But you cannot remove Container disk5 (H2) by itself because it's the first Container on that drive (regardless of the numbering). You would have to remove Container disk4 (Nelson) before removing Container disk5 (H2). When you create partitions they are created first-to-last but to remove them you have to go last-to-first.

OTOH if you merely want to erase H2 without repartitioning the drive you would select & erase Container disk5 not H2. You format the container, which in turn creates the "drive."

As always, make sure you have a good backup first.

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Answer 3

nelsonmay Author

Level 1

29 points

Sep 23, 2026 5:36 AM in response to MartinR

I wished I would have been able to read the post my Martin R. I do have a Time Machine backup, but I am going to start from scratch. I may not be this deep in now. This is an older Mac to run older versions of Pro Tools.

Anyway,

I screwed up this mac and could use some help. I erased my partitions by deleting the volumes and this may have started the cascade. Basically, anything I do now I get the folder with the question mark when I start the mac. From reading, I think it is confused and can’t find a start up disk.

This is a 2009 8 Core 2.26Ghz Mac Pro, 16GB Ram, 500GB SSD (MB535LL/A) that started with Leopard. I tried to put in the leopard DVD and it wouldn’t install the OS. I did flash the bios a few years ago so I could get this thing up to High Sierra. Anyway, I took out the boot SSD, reformatted it with my M3 mac Book, OS Journaled, etc., copied 10.13.0 and the 2009 still can’t find the boot disk. I tried holding the option key and Command R keys. Nothing. I also reset the Ram and PRAMM, at least I think I did. It chimed twice when I did it.

By the way, I have a version of High Sierra that has worked in the past on this mac. 10.13.0. I have a copy and tried to make a USB boot drive with the 10.13.0. I don’t understand how to add the proper path to this command in terminal.

sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

I named my USB drive boot USB and the name of the HS 10.13.0 installer is called Install macOS High Sierra.app. Somehow I saved a file called InstallOS.dmg which is also High Sierra. (that didn’t work on the boot USB drive.)

…I also have copies of mavericks, Yosemite and el capitan. I don’t think I can go higher than High Sierra.

If the is any advice you can give me, great. I live near an apple store and may see if the genius bar can help me if I can’t get this thing working at home.

Cheers!

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Answer 4

Sep 23, 2026 7:04 PM in response to nelsonmay

First, according to the MacTracker app, there are no 2009 Mac Pros (desktop system) which officially supports macOS 10.13 High Sierra. Even a 2009 model MacBook Pro does not. If your "Mac Pro" is either of these two models, then you are/were using a hack which Apple won't allow us to discuss on these forums. If you were using a hack, then you may first need to perform a PRAM Reset in order to clear the PRAM/NVRAM of any special boot options required by that hack as they are likely incompatible with booting a supported version of macOS.

In order to create a bootable macOS USB installer, people need access to a working Mac which is actually compatible with the OS they want to create (the Mac can currently be running any version of macOS 10.6+). With a compatible qualifying Mac, people can use the instructions in the following Apple article for create a bootable macOS USB installer (there is a link within that article for downloading various versions of the macOS installer):

Create a bootable installer for macOS - Apple Support

For a 2009 Mac Pro (or even MBPro), you will need access to a working Mac running macOS whose model designation is generally 2007 to 2015 to create a bootable macOS 10.11 El Capitan USB installer which is the last compatible version of macOS for a 2009 Mac Pro.

If you have the 2009 Mac Pro desktop tower, then you could also start with a retail copy of the OS X 10.6 Snow Leopard Upgrade DVD (one with a picture of the cat on it). Then you will to use any other computer or OS (macOS, Windows, Linux) to download the El Capitan DMG installer archive and copy that DMG to the Snow Leopard installation so you can extract the real El Capitan installer app into the Applications folder (double-click the .pkg file) where you can then run the real El Capitan installer located in the Applications folder to upgrade the system from Snow Leopard to El Capitan.

These are the only options we can suggest to you since El Capitan is the last officially supported OS for a 2009 Mac Pro (or MBPro).

FYI, there is no Internet Recovery Mode for systems that cannot be officially upgraded beyond El Capitan. macOS 10.7 to 10.11 (and some models supporting 10.12 or even 10.13) only have access to the local Recovery Mode which accesses the Recovery Partition hidden on the macOS boot drive of macOS 10.7 to 10.11 (10.12/10.13).

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