Why can't I partition this external drive?

Why is "partition" grayed out? I want to partition this SSD and use half for Time Machine backup, half for drag n drop storage. I already tried erasing and I'm unclear why it still says 827 MB is being used.





[Edited by Moderator]

MacBook Air 13″

Posted on Jul 5, 2025 6:14 PM

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Posted on Jul 5, 2025 7:33 PM

Based on your screen shot it’s formatted with Master Boot Record which does not support partitioning. Reformat the Device to HFS+ or APFS and use GUID Partition Map instead of Master Boot record.


Another thing, what version of macOS are you running on your MBA? If it’s Big Sur or later you cannot use it as a Time Machine volume unless it’s formatted as APFS. In addition most volunteers here always recommend that the Time Machine volume be dedicated to Time Machine only, not shared with other data.


APFS formatted drives negate the need for classic partitioning as well. You can create as many volumes as you want within the main ‘container’. If you insist on using the SSD for two purposes then format it as APFS and create two volumes.


So what version of macOS are you running pn your MBA?

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Jul 5, 2025 7:33 PM in response to bananastand2023

Based on your screen shot it’s formatted with Master Boot Record which does not support partitioning. Reformat the Device to HFS+ or APFS and use GUID Partition Map instead of Master Boot record.


Another thing, what version of macOS are you running on your MBA? If it’s Big Sur or later you cannot use it as a Time Machine volume unless it’s formatted as APFS. In addition most volunteers here always recommend that the Time Machine volume be dedicated to Time Machine only, not shared with other data.


APFS formatted drives negate the need for classic partitioning as well. You can create as many volumes as you want within the main ‘container’. If you insist on using the SSD for two purposes then format it as APFS and create two volumes.


So what version of macOS are you running pn your MBA?

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Jul 5, 2025 9:00 PM in response to bananastand2023

How do I format in APFS when that's not one of the 4 available options under the Erase menu?

If it's not available it is because it isn't in a GUID partition map. From your second screenshot, it was in Master Boot Record (MBR)--an old Windows partition scheme. Without showing all Devices, you can't change the device formatting, only the existing volume.

You need Erase the device and select GUID Partition Map in the Erase window in order to have APFS available.

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Jul 6, 2025 1:26 PM in response to lkrupp

lkrupp wrote:

You have no idea what you are talking about. The original poster wants to use the drive as a Time Machine volume and ExFAT will not work.

Not every disk is suitable for a Time Machine. Properly selected things should be used.

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Jul 6, 2025 6:37 AM in response to bananastand2023

bananastand2023 wrote:

Why is "partition" grayed out? I want to partition this SSD and use half for Time Machine backup, half for drag n drop storage.

First of all, you don't want to do that. Attempting to partition a Time Machine volume is something that people always regret - always.


But if you want to prove my point, what you need to do is go to the View menu in Disk Utility and tell it to "Show all volumes". Then, you will be able to erase the physical disk and partition it in a manner that's more likely to cause you misery.


For Time Machine, format to HFS+. Then point Time Machine at the drive and it will convert it to APFS.

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Jul 6, 2025 10:50 AM in response to etresoft

The OP has tried formatting a number of times using Master Boot Record. They’ve been told repeatedly that they need to use GUID Partition Map instead in order for there to be a ‘partition’ option available. They either don't understand or are unable to follow instructions. They don’t appear to understand the difference between a device and a volume on that device. I don’t what else we can do to explain.


Maybe someone can create a screen recording showing exactly how to do this. I’m not willing to.

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Jul 6, 2025 4:15 PM in response to olavi145

olavi145 wrote:


lkrupp wrote:

You have no idea what you are talking about. The original poster wants to use the drive as a Time Machine volume and ExFAT will not work.
Not every disk is suitable for a Time Machine. Properly selected things should be used.

My current working solution: Unitek Y-3363 + Samsung SSD 860 PRO 1TB (APFS (Case-sensitive))



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Jul 6, 2025 5:38 PM in response to olavi145

olavi145 wrote:


lkrupp wrote:

You have no idea what you are talking about. The original poster wants to use the drive as a Time Machine volume and ExFAT will not work.
Not every disk is suitable for a Time Machine. Properly selected things should be used.

I’ve never met one that doesn’t work. Maybe I don’t get out enough.

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Why can't I partition this external drive?

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