“Merging” internal drive with external drive running same OS different version Monterrey

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“Merging” internal drive with external drive running same OS different version Monterrey

What can I do to have both drives “merged” correctly. One is labeled “storage” and it used to be the boot drive until I changed the boot drive to an external SSD. However, now the external boot drive is updated to the latest version of Monterrey, while the internal “storage” one is not. Hence, there are two separate sets of system folders for “Applications”, “Images”, “Music” etc which follow from MacintoshHD normally. Don’t really care about the other folders, but as there seem to be two different photo libraries of different sizes, if I update the internal storage drive to the latest version of Monterrey, will everything “merge” itself seamlessly, or would it overwrite the folders on the external boot drive? (which would be bad) thanks for the input.

iMac 21.5″

Posted on Nov 2, 2025 3:50 AM

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Answer 1

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Servant of Cats

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Nov 2, 2025 4:58 AM in response to RaggedNuggetBandit

Assuming that you are not using iCloud Photos now, upgrading the version of Monterey on the internal drive will not merge your Photo libraries. There will continue to be two different Photo libraries, one on each drive.

So I don't think you will be overwriting the folders on the external boot drive. (When doing the upgrade, you could boot from the internal drive, and detach the external one before you start the upgrade, if it made you feel safer. It would be rather hard for any program to write to an "air-gapped" drive!). But you won't be merging the two sets of data (seamlessly or otherwise), either.

One possible way of merging the Photos libraries. Warning: This might create duplicates that you would need to delete by hand. Hopefully not, but I make no guarantees. After you update Monterey on the internal drive, and if you have enough iCloud/iCloud+ space,

Boot from the external drive that you want to turn into a "storage" drive, turn on iCloud Photos, and wait until your Mac has fully synchronized its Photos library with iCloud.
Turn off iCloud Photos, for the Photos library on that drive, in a way that does not delete photos from iCloud.
Boot from the internal drive, turn on iCloud Photos, and let the Mac synchronize the local Photos library with iCloud.

Note: When using iCloud Photos, you can force the Mac to "Download and keep originals", or you can allow it to "Optimize" storage (means some local copies of photos might be lower-quality "space-saving" copies). I prefer keeping full-size originals, because then I know that local backups contain full-size originals.

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