Sequoia 15.4 not installing on my external Samsung T7 2TB boot drive

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Level 1

10 points

Sequoia 15.4 not installing on my external Samsung T7 2TB boot drive

my iMac 24-inch, M1, 2021 has a 245GB internal SSD and before running out of memory I created a boot drive running OS 15.3.2 on a Samsung T7 SSD with 2 TB. It's been working fine for a couple of weeks and I decided to update the T7 to OS 15.4. The installation behaved normally yesterday so I left the iMac and returned this morning to find the installation apparently ended. But the OS remained 15.3.2. I ran the update again and monitored it till the end at which time the iMac/T7 restarted.... to OS 15.3.2. The original internal HD is also still 15.3.2. I'm looking for a solution or at least an answer like: you cannot update to an external SSD boot drive.

iMac 24″, macOS 15.3

Posted on Apr 6, 2025 5:05 PM

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Answer 1

steve626

Level 6

13,791 points

Apr 6, 2025 8:52 PM in response to Rob Fuentes

Apologies is this seems obvious, but have you verified unambiguously which drive your Mac is actually booting from now? What I am wondering is if the computer is booting from the internal drive now? Why would it do that? Well, it might be that there is some issue with the external boot drive now after that update, or it might be simply a matter of re-asserting in Settings that the boot drive is to be the external drive, not the internal drive.

If none of the above applies, then there may be something more complex going on.

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Answer 2

Rob Fuentes Author

Level 1

10 points

Apr 9, 2025 6:16 PM in response to steve626

To steve626, the Systems Settings>General>Start Up Disk highlighted thr T7 drive. Both internal and external drives are running OS 15.3.2.

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Answer 3

steve626

Level 6

13,791 points

Apr 9, 2025 8:46 PM in response to Rob Fuentes

There are a variety of reasons why an external drive no longer boots the Mac. For instance, ONE EXAMPLE (maybe does not apply to you) is

Determine which disk started up your Mac - Apple Support

However in the Apple Support Communities are numerous posts from users who had an external bootable disk but had trouble updating it. It's not just you and it's unclear how to resolve it. There are yet another whole family of postings from other users who ran into difficulty updating to 15.4. It seems to depend on the individual configuration on the Mac. My work Mac upgraded to 15.4 with no issues. I have been holding off on my personal Mac as I am still doing income taxes and won't change anything until those are all completed and filed.

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Answer 4

tbirdvet

Level 6

17,090 points

Apr 10, 2025 5:13 AM in response to Rob Fuentes

Not sure why some are having issues using an external drive. I have 3 Mac's. All are running 15.4 on the internal. I made an external TB drive for each Mac to boot from (I use for testing primarily) and have no issues. I always start in Recovery, install the OS then use Carbon Copy Cloner to transfer my data to the external drive. All drives are formatted APFS and all are thunderbolt drives. I use WD NVME drives in Acasis and Trebleet enclosures. With each OS update I just boot from the external and update the system as any normal update process. I have never had any issues. This works on my Silicon and Intel Macs.

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