External Startup Disk is Not Working

[raythompsontn]

I have created, I think, an external startup disk for my M4 Pro MacBook Pro. I have followed the instructions on the Apple support site. I downloaded MacOS Sequoia from the App Store. I connected to the SandDisk 1TB SSD to the non-DFU port and formatted the external disk as APFS using the Disk Utility. I selected that drive onto which MacOS should be installed. I followed these instructions.

Install macOS on an external storage device and use it as a startup disk - Apple Support

If you have an external storage device, you can set it up as a Mac startup disk.

support.apple.com

All seemed to go OK. I then restarted my Mac, held down the power button on the upper right of the keyboard. I get the startup options with the MacOS disk on the MacBook, the external startup disk that I just created, and the settings icon. I click on the external disk that I created and nothing happens other than the Continue button dimming.

What am I missing?

 

[Adora]

Have you cloned it? Or reinstalled? Cloning never worked for me to boot. It always stopped at the beginning of the progress bar. With a reinstall it worked.

Also only Thunderbolt connections really work reliably. Do you use USB maybe?

At least there was a warning in Carbon Copy Cloner not to use USB. With 15.2 you can't even clone a boot drive anymore.

I just used the macOS full installer from the internal drive and after the installation the Migration Assistant, that worked fine with a TB4 connection.

This was on an M3 iMac with some beta of 15.1 or 15.2 I think. Cloning the drive with Super Duper or CCC was before 15.2 when it still worked, but it couldn't really boot for some reason.

Sorry for editing my post that much. I didn't want to spam the thread with new ones.

 

[raythompsontn]

Have you cloned it? Or reinstalled?

I did a full install using the instruction from Apple.

Do you use USB maybe?

USB-C all the way. No adapters.

With 15.2 you can't even clone a boot drive anymore

I am running 15.3.

that worked fine with a TB4 connection

The Mac has TB5.

I am using this drive as the external drive.

https://www.amazon.com/SanDisk-2TB-Extreme-Portable-SDSSDE61-2T00-G25/dp/B08GTYFC37/ref=sr_1_3?crid=35QYSD1W0QHUB&dib=eyJ2IjoiMSJ9.Kmk76mCDHDZULOvKiIeJyfsYMuATlgN7FCyvYg_PATRnsEfH0wTxGjmkX4e9PAVuXYufeFawQXuuQTP82aPIADPd5QY1S-L_T2DJk8EPZY46x3QMSd4E3JRlCVpa8O3RBDo72eG3vynGQhMHB9HOoqyRk93_BDuriZI4aW3f9ZuOsKQgAQMrdD0tOvzEpPbEZW9VnAatcfmtKJ5VR9D18al2o90roPUeWnebXrueifc.6-p-suqjliiGKLbr_iElZU_JdctuJwqurLloc9ahYpw&dib_tag=se&keywords=sandisk&qid=1736700551&sprefix=sandisk%2Caps%2C105&sr=8-3&th=1

 

[Adora]

I did a full install using the instruction from Apple.

USB-C all the way. No adapters.

I am running 15.3.

The Mac has TB5.

I am using this drive as the external drive.

https://www.amazon.com/SanDisk-2TB-Extreme-Portable-SDSSDE61-2T00-G25/dp/B08GTYFC37/ref=sr_1_3?crid=35QYSD1W0QHUB&dib=eyJ2IjoiMSJ9.Kmk76mCDHDZULOvKiIeJyfsYMuATlgN7FCyvYg_PATRnsEfH0wTxGjmkX4e9PAVuXYufeFawQXuuQTP82aPIADPd5QY1S-L_T2DJk8EPZY46x3QMSd4E3JRlCVpa8O3RBDo72eG3vynGQhMHB9HOoqyRk93_BDuriZI4aW3f9ZuOsKQgAQMrdD0tOvzEpPbEZW9VnAatcfmtKJ5VR9D18al2o90roPUeWnebXrueifc.6-p-suqjliiGKLbr_iElZU_JdctuJwqurLloc9ahYpw&dib_tag=se&keywords=sandisk&qid=1736700551&sprefix=sandisk%2Caps%2C105&sr=8-3&th=1

The problem could be that the drive only has a USB 3.2 connection. I read you need Thunderbolt 3-5 on both sides for real compatibility.

I am not sure if it doesn't work at all. It least it's not recommended to use USB.

Were you able to get in the security settings of your external drive and is it set as permanent startup drive?

I also have SIP disabled on my iMac. I don't know if you need to do that but I don't think so.

 

[Mike Boreham]

I have created, I think, an external startup disk for my M4 Pro MacBook Pro. I have followed the instructions on the Apple support site. I downloaded MacOS Sequoia from the App Store. I connected to the SandDisk 1TB SSD to the non-DFU port and formatted the external disk as APFS using the Disk Utility. I selected that drive onto which MacOS should be installed. I followed these instructions.

Install macOS on an external storage device and use it as a startup disk - Apple Support

If you have an external storage device, you can set it up as a Mac startup disk.

support.apple.com

All seemed to go OK. I then restarted my Mac, held down the power button on the upper right of the keyboard. I get the startup options with the MacOS disk on the MacBook, the external startup disk that I just created, and the settings icon. I click on the external disk that I created and nothing happens other than the Continue button dimming.

What am I missing?

View attachment 2471671

It really should have worked as you seem to have done everything right. In the early days of Silicon external booting was very flaky and I sometimes found that doing the same thing again worked second time, perhaps a different lead, (as the only thing easy to change).

All I can contribute is that you do not to disable SIP, or reduce Startup Security or use a Thunderbolt drive. I have used the Apple method on a Samsung T5 recently and it worked. Thunderbolt is preferable because it is faster and SMART and TRIM are supported, but not essential. I have made many external boot drives since Silicon but I have not personally used a Sandisk one, but would expect it to work.

The macOS 15.2 problem is about cloning because it has to use ASR (Apple System Replicator) for the SSV and ASR seems to have a bug. So the macOS 15.2 issue is not relevant to you.

 

[genexx]

There is now way to start / Boot from this disk without a certified Thunderbolt Cable, and no, the one is delivered with this drive is not one.

I would also not try to use this disk as boot drive, because it is slow and you can be very sure this does not work in any good way.

What works and is fast enough, is an Acasis TBU405 AIR or better Thunderbolt Case with a WD SN770 or WD SN850x NVME.

The Thread for this.

 

[raythompsontn]

I would also not try to use this disk as boot drive, because it is slow and you can be very sure this does not work in any good way.

I realize that the drive would be much slower than the internal drive. I was not creating the drive to actually use the drive. I just wanted to see how it all worked. In this case, not.

 

[raythompsontn]

There is now way to start / Boot from this disk without a certified Thunderbolt Cable, and no, the one is delivered with this drive is not one.

I tried a Thunderbolt 5 cable, from Apple. The drive cannot even be formatted as APFS as I get an operation failed.

 

[raythompsontn]

I sometimes found that doing the same thing again worked second time

I have tried three times with the same result. A couple more and it would border on insanity doing the same thing over and and over and getting the same result.

Ah well, it was just an experiment to see how it is done and if it is even viable. I don't want to spend a lot of money to get another, expensive enclosure and drive, just to satisfy my curiosity.

 

[bogdanw]

Try in another port.
Apple Silicon's hidden restrictions drove me mad while trying to install Sequoia on an external drive. It failed repeatedly with no error, just boot loop. I had to select to copy my account when the installation started, then to create a new account when the installation finished.

 

[raythompsontn]

Try in another port

I did. Although the Apple instructions state specifically to not use the DFU port. That is the one port I have not tried.

 

[Bigwaff]

Some great resource here.

Search Results for “boot external” – The Eclectic Light Company

Macs, painting, and more

eclecticlight.co

 

[Mike Boreham]

I tried a Thunderbolt 5 cable, from Apple. The drive cannot even be formatted as APFS as I get an operation failed.

That really surprises me. I have a mix of USB 3 and Thunderbolt 3 drives and have standardised on TB3 leads for simplicity. So my USB SSD's always get connected with a TB3 lead. I have never had trouble formatting a drive. I would expect TB5 to be backwards compatible with TB3 and behave the same with a USB 3 drive as TB3 cables do….maybe that is wrong.

 

[Adora]

It really should have worked as you seem to have done everything right. In the early days of Silicon external booting was very flaky and I sometimes found that doing the same thing again worked second time, perhaps a different lead, (as the only thing easy to change).

All I can contribute is that you do not to disable SIP, or reduce Startup Security or use a Thunderbolt drive. I have used the Apple method on a Samsung T5 recently and it worked. Thunderbolt is preferable because it is faster and SMART and TRIM are supported, but not essential. I have made many external boot drives since Silicon but I have not personally used a Sandisk one, but would expect it to work.

The macOS 15.2 problem is about cloning because it has to use ASR (Apple System Replicator) for the SSV and ASR seems to have a bug. So the macOS 15.2 issue is not relevant to you.

Any USB drive I ever tried with whatever connection, with or without external power auto-ejects at least once a day or regularly every few hours. I can't even count the drives and cable combinations I tried.

What happens if I use this as a boot drive? This never ever happened with a Thunderbolt 3 or 4 drive, that is even powered by the port and can be used on a Dock or directly on the Mac without any problems.

I have two that even have an integrated fan that gets activated when pushing a button. The fast drives can get very hot. But I never needed it when using an external 4TB drive on my M3 iMac. I got wrong cases that only supported half the speed of the drive. But it somehow felt faster than the internal drive. In Blackmagic it was almost the same.

 

[Adora]

Some great resource here.

Search Results for “boot external” – The Eclectic Light Company

Macs, painting, and more

eclecticlight.co

That website is really great. It's even worth another post.

 

[Adora]

I bought those enclosures by the way and the cheapest about 7.000 read/write drives I could get and all worked fine with the included cable. Here it says TB3, mine has TB4 printed on it. Maybe they sold different ones. Or there is no difference. I still don't understand the difference between TB3 and TB4, I think at least for speed there is none maybe for displays or power delivery. It seems I have to read about that.

Anyoyo 40Gbps M.2 NVMe to USB C Built-in Fan SSD Enclosure

Triple Cooling: The upgraded EC6902 Pro has a built-in cooling fan with an aluminum alloy case and silicone cooling pads for precise heat conduction. The heat dissipation effect is 30% higher than other hard disk enclosures.Tool-free Installation: No screw or screwdriver needed, equipped with...

www.anyoyo.com

Maybe they have faster ones now. I found them on Amazon. With and without fan and all four included a short TB4 cable.

I like the material because it's metal and absorbs the heat very good.

Sadly I didn't know TB5 is just around the corner. Didn't expect it already in the next years.

 

[Mike Boreham]

Any USB drive I ever tried with whatever connection, with or without external power auto-ejects at least once a day or regularly every few hours. I can't even count the drives and cable combinations I tried.

This is not typical. Many people use external USB SSD as their daily driver.

I am not saying that Thunderbolt isn't better for external booting only that it isn't necessary. Personally if were creating an external boot drive as my daily driver I would use Thunderbolt.

 

[Adora]

This is not typical. Many people use external USB SSD as their daily driver.

I am not saying that Thunderbolt isn't better for external booting only that it isn't necessary. Personally if were creating an external boot drive as my daily driver I would use Thunderbolt.

I also booted very often from external USB drives in earlier times. Don't know if it's Apple Silicon or the many USB 3.x versions now, but something got worse. I was also never a friend of APFS. I also often can't eject drives when I want to, because they are somehow in use, but they are not. And since APFS the file system corrupts much easier when a drive was not properly ejected.

There was also this warning not to use USB as boot drive in Carbon Copy Cloner for a legacy boot drive cloning option. I have to look if I find it again because it now got replaced by a text that since 15.2 boot drive cloning isn't possible at all anymore.

 

[Fishrrman]

You don't "have to have" thunderbolt.

USB3 will do.
Or USB3.1 gen2.

 

[genexx]

I tried a Thunderbolt 5 cable, from Apple. The drive cannot even be formatted as APFS as I get an operation failed.

There are plenty of USB Drive Chipsets that simple do not work with Mac.
Your Drive seems to have one of them.
I had an External Enclosure where only the WD SN770 worked and the WD SN850x did not for some mysterious reason when connected to MBA M2.
And the Enclosure was with the high compatibel RTL Chipset, but worked flawless on Intel Mac.

I have tried to install on the USB Drive and it crashed while booting after Install.
I use now the Acasis TBU405 AIR Thunderbolt JHL7440 Chipset Case with WD SN770 2TB.
This works.

 

[raythompsontn]

There are plenty of USB Drive Chipsets that simple do not work with Mac.
Your Drive seems to have one of them.

That seems to be the most logical explanation so far. Even though the drive works well for storing files and as a Time Machine device (I have two of them). Everything works that I have tried except booting from the drive.

Because of that I think it is a driver issue. The needed drivers are loaded when using MacOS but are not available when trying to boot as the drivers are not yet available.

Someone once told me that many things work easily on a Mac. Other things are impossible to figure out why they don’t work. I am finding that to be a very true statement.