Installing Big Sur on external SSD. What format?

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Installing Big Sur on external SSD. What format?

I have just downloaded the Big Sur OS Installer. Big Sur is to serve as a second OS, so I had prepared an external SSD to install it on. All I've read says that after Sierra (10.12.6) one needs to use APFS, so I'd formatted my external SSD APFS. I've just tried to install the downloaded Big Sur OS on that drive but get the message that that drive has to be formatted MAC OS Extended (Journaled). This is confusing me. The computer that I used to download Big Sur and that I'll be using Big Sur on as a second OS is a 2017 5K IMac running Sierra, so that IMac's boot drive is MAC OS Extended (Journaled). Is this why I'm being told that the external SSD that will be attached to this computer must also be MAC OS Extended (Journaled)? But what then of all I've read that says all OS after Sierra must run with APFS?

Thanks.

John

iMac (2017 – 2020)

Posted on Apr 19, 2023 1:13 PM

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Answer 1

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VikingOSX

Level 10

128,156 points

Apr 19, 2023 2:16 PM in response to campbellstreet

If you downloaded the full Big Sur installer and created a bootable USB stick from that installer, then you boot (option key) from that USB source so the currently running operating system (Big Sur) understands APFS (implicitly case-insensitive) drive formatting. If you booted from Sierra, that operating system had no clue about APFS formatting and you will only be offered the macOS Extended Journal format.

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Answer 2

Apr 19, 2023 2:58 PM in response to VikingOSX

Hi.

Thanks for the reply.

I'm afraid I don't fully understand what you say.

To download the Big Sur installer I had to use some computer so used the computer I'll be using it on as a second OS - the one operating on Sierra OS. It's when I did that what I described in my first post occurred. That is, I reached a point where I could not install the OS on my external SSD while it was formatted APFS. (I removed that drive and reformatted in as MAC Extended OS (Journaled), connected it once more to the above computer and i was able to install Big Sur on it. Having done that I'm now able to access either OS -Sierra or Big Sur - by holding Option key while booting the computer or by going to "Strat Up Disk" in Preferences.)

I assumed that what I'd done in this process was create what you call a "bootable USB stick", only in my case it is a "bootable external SSD".

Seems you are saying that my Big Sur, though installed on a Mac Extended OS (journaled) drive will "understand APFS drive formatting"; that is that the fact the OS itself is on a Mac Extended OS (journaled) drive is not important. Presumabley it will be able to understand both Mac Extended OS (journaled) files and APFS files, as files and apps I download onto this OS will be on that Mac Extended OS (journaled) boot drive.

John

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Installing Big Sur on external SSD. What format?

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