Adding a new SSD prevent loading MacOS on the first one

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Adding a new SSD prevent loading MacOS on the first one

Hi,

I have an iMac from 2013 with MacOS 10.15.7. Since the internal hard drive is slow, i have installed the MacOS on a 2To external SSD. So far so good : everything looked great and my computer worked fine.

I recently add a new 4To SSD using an USB3 port of my iMac.

When i start now my computer, the boot disk is not recognized anymore and a black screen appears. When i disconnect the new 4To SSD, eveything works well again...

Since i would like to be able to leave the new SSD connected to my computer when i start it up, what should i do ?

I have tried to reinstalled MacOS on the internal hard drive but it did not change anything. So i uninstalled it again.

Any suggestion that could help will be highly appreciated :-)

As you can see, all SSD has been erased using APFS format with GPT :

Posted on Dec 5, 2021 1:48 AM

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Answer 1

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PRP_53

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86,719 points

Dec 5, 2021 6:43 AM in response to skrabidou

The issue appears to be the Computer does not see the additional External Drive when the External Drive is using the USB-A or USB -C connection on the computer.

If a Self Power Enclosure, where the External Drive is placed. The Power Adapter to wall Socket for electricity and then to Enclosure will make the External Drive NOT Depend on the USB-A/C on the computer connect for power.

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Answer 2

skrabidou Author

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Dec 5, 2021 4:48 AM in response to PRP_53

Thanks for your answer.

However, there is only one bootable drive since i erased the internal drive.

See below what shows the Boot menu in the System preferences when both SSD are connected :

As far as i see, i can operate no Drive changes from here which looks correct since only one drive is bootable...

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Answer 3

PRP_53

Level 10

86,719 points

Dec 5, 2021 2:50 AM in response to skrabidou

Would suggest

1 - Have only the Bootable Drive contains Catalina attached to the computer when it does a Cold Boot.

2 - The addition Drive be connect to a Self Powered Enclosure and then connect to computer while doing a Cold Boot.

This is something I can not explain in Catalina and above that booting from Bootable External Drive ( Main Drive with Catalina installed ) where it will perform as you have describe - Not boot with two or more USB Connect External Drive .

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Answer 4

skrabidou Author

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Dec 5, 2021 3:19 AM in response to skrabidou

I precise that i switched the USB port between the two SSD but it did not work better.

I also started the computer in Recovery mode and tried to change the boot disk, but no boot disk appeared...

How can i tell my Mac to keep starting on the 2To SSD when the 4To SSD is connected while the Mac does not see the first SSD anymore ?

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Answer 5

PRP_53

Level 10

86,719 points

Dec 5, 2021 4:33 AM in response to skrabidou

Restarting in Recovery Mode will have no effect on the issue.

In System Preferences >> Startup Disk with the Bootable Installation Drive attached and change for Internal Drive to External Drive will have the computer automatically try to Cold Boot to External Drive.

This must be performed from the Admin Account of this computer.

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Answer 6

PRP_53

Level 10

86,719 points

Dec 5, 2021 4:49 AM in response to skrabidou

Please - re-read the earlier posting with suggestions.

1 - Have only the Bootable Drive contains Catalina attached to the computer when it does a Cold Boot.

2 - The addition Drive be connect to a Self Powered Enclosure and then connect to computer while doing a Cold Boot.

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Answer 7

skrabidou Author

Level 1

8 points

Dec 5, 2021 5:16 AM in response to PRP_53

Sorry, but my english as well as my computer skills seem to be not good enough to understand what you asked...

When you say :

1 - Have only the Bootable Drive contains Catalina attached to the computer when it does a Cold Boot.

To me, this is a "normal" boot... I don't understand why you call that a "Cold" boot... If i have to do something to start a "Cold boot", please let me know. I have searched "Cold boot" on the internet, but i could not find any helpful information...

You also wrote : "In System Preferences >> Startup Disk with the Bootable Installation Drive attached and change for Internal Drive to External Drive will have the computer automatically try to Cold Boot to External Drive".

-> As you could see on last screen capture, i can't "change for Internal Drive to External Drive" since there is no Internal Bootable Drive...

2 - The addition Drive be connect to a Self Powered Enclosure and then connect to computer while doing a Cold Boot.

What do you mean by "The addition Drive be connect to a Self Powered Enclosure" ? My SSD has only an USB connection...

Sorry again for my lack of comprehension !

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Answer 8

skrabidou Author

Level 1

8 points

Dec 5, 2021 7:01 AM in response to PRP_53

Thanks for your answer !

So my problem comes from the Power supply of my SSD using the USB connexion and from my computer which is - for any reasons - unable to feed two SSD when starting up...

It looks like there is no solution since my SSD can't be powered by an external electricity source with the Hard Drive Enclosure i use (Ugreen CM237)... Good to know !

Thanks again for your help and the time you spent for all these explanations !

Best regards

Edit : isn't any possibility to "mute" an external drive when starting the computer and "turn it on" after MacOS has launched ?

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