SSD erased when switching startup disk from Mojave to El Capitan.

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SSD erased when switching startup disk from Mojave to El Capitan.

Currently running 10.11.6 on late 2012 iMac and wanted to test some old SW before upgrading to Mojave. Cloned 10.11.6 onto external SSD, restarted from it and installed latest version of Mojave on ssd. After finishing my tests, I rebooted to El Capitan and SSD was wiped! Disk utility indicated SSD was not even initialized. Tried same process again with same results. Could this have something to do with Mojave install changing SSD file system to apfs, which wouldn't be recognized when I rebooted into El Capitan? If so, any way around this? I would like to have a Mojave sandbox but don't want to spend 3-4 hours creating one that only lasts for one restart.

Peter D.

iMac 21.5", OS X 10.11

Posted on Feb 23, 2020 7:35 AM

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Answer 1

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SXMPETE Author

Level 1

8 points

Feb 25, 2020 7:13 AM in response to DonH49

Installing Mojave on external SSD resulted in an APFS drive that could not be recognized when I rebooted back into El Capitan (HFS+). SSD wasn't really erased, just not recognizable by an OS that predates APFS.

Workaround was to boot with option key, and select external SSD as boot drive - problem solved!

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Answer 2

DonH49

Level 6

16,704 points

Feb 23, 2020 7:54 AM in response to SXMPETE

If you directed Mojave to install onto that SSD and even if it was HFS+ then yes its going to be transformed into APFS.

I don't understand the 4 hours mention for sandboxing.

I would use my Mojave external drive and boot from it and use Disk Utility to APFS on the SSD. This should take about 5 minutes max. Then proceed with the Mojave install , a less than 20 minute install. Assuming you have the proper software and external device.

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SSD erased when switching startup disk from Mojave to El Capitan.

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