User profile for user: Thomas Ernst
Thomas Ernst Author
User level: Level 1
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Mac Studio M1 Max: Cannot partition boot drive

I cannot partition my boot drive.

I have a Mac Studio M1 Max, 1Tb SSD. 446 Gb is used.


I am running Ventura. I want to create a small partition (50Gb) to house a copy of Ventura from which I can continue to run a legacy app that won't run beyond OS13.

And then I can upgrade my main OS to Sequoia.


If I boot into recovery, and run Disk Utility, I have no access to the "+" button. Screenshot attached shows the OS is refusing to resize the partition. (I have booted into disk util on my wife's mac studio, and the "+" is available).


I also, after considerable blood sweat and tears, got my mac to boot from an external drive, but I encountered the same blockade in adding a partition.


The only way I see going forward is to boot off the external drive, erase my boot drive, partition it to a 945Gb primary OS and 50Gb secondary OS, and then restore my (superduper) backup to the primary OS partition.


I hate the nuclear option, so I'm wondering if I've missed something.


TIA

tom

Mac Studio (2022)

Posted on Jan 3, 2026 10:18 AM

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User profile for user: D.I. Johnson
D.I. Johnson
User level: Level 7
33,347 points

Posted on Jan 3, 2026 11:40 AM

Thomas Ernst wrote:

thanks! (I guess partitioning is for pre-APFS formats? would make sense as the last time I partitioned a drive was probably 15+ years ago)

You're welcome.


Yes, Apple's APFS format has changed and improved the way storage is managed since it was introduced with High Sierra (?). APFS is the new default and standard for macOS, though you can still use older formats for storage.


On an APFS formatted drive, additional volumes may added to or deleted from a container without having to reformat or repartition the drive. APFS volumes share the whole of the storage capacity of the container and can dynamically grow or shrink as their storage requirements change. 


If you wish, volume sizes can be managed by setting storage reserves and/or quotas when creating a volume. Adding and deleting APFS volumes is faster and simpler and safer than editing a partition map.


Use Disk Utility to manage the APFS formatting of drives and the creation and deletion of volumes within the containers on those drives.


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


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Question marked as Top-ranking reply
User profile for user: D.I. Johnson
D.I. Johnson
User level: Level 7
33,347 points

Jan 3, 2026 11:40 AM in response to Thomas Ernst

Thomas Ernst wrote:

thanks! (I guess partitioning is for pre-APFS formats? would make sense as the last time I partitioned a drive was probably 15+ years ago)

You're welcome.


Yes, Apple's APFS format has changed and improved the way storage is managed since it was introduced with High Sierra (?). APFS is the new default and standard for macOS, though you can still use older formats for storage.


On an APFS formatted drive, additional volumes may added to or deleted from a container without having to reformat or repartition the drive. APFS volumes share the whole of the storage capacity of the container and can dynamically grow or shrink as their storage requirements change. 


If you wish, volume sizes can be managed by setting storage reserves and/or quotas when creating a volume. Adding and deleting APFS volumes is faster and simpler and safer than editing a partition map.


Use Disk Utility to manage the APFS formatting of drives and the creation and deletion of volumes within the containers on those drives.


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


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Mac Studio M1 Max: Cannot partition boot drive

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