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Old 02-01-2020, 03:09 PM
Darryl Ramm Darryl Ramm is offline
Join Date: Nov 2010
Location: USA
Posts: 14,238
Default Re: Installing older OSX onto external HD to run earlier PT version?

No info on what iMac you have.... which would have been useful.

If your sessions will stay on the current internal boot/system drive you can leave them there. As long as you are not trying to boot an older version of macOS/OS X that does not support the APFS filesystem that the internal drive likely uses. Just going back to Mojave is fine.

Do **not** use the system migration assassin (assistant) to migrate apps or drivers, from your current boot disk. You need to reinstall all that again on the external drive, including Pro Tools, ILM, and you should also reinstall all your plugins... if they are compatible with what's installed on the other drive you can set them up to point to the sample libraries on the internal drive. **Do** use the system migration assassin to move/copy your user account from the internal to external drive... or do this manually, but you have to make sure that the user id (not just name) on the accounts match or you will have all sorts of problems. You could set up the home directory only say being on the internal drive, or two separate home directories one on each boot drive... either way you need to make a decision where all your personal files, sessions etc. are going and how you are backing them up.

If you want as fast a boot/app start etc. experience as on an a recent iMac internal SSD then you need an external Thunderbolt 3 NVMe/PCIe 3 SSD. Like the Samsung X5. Like the internal PCIe/NVMe SSD these are much faster than a SATA SSD.... but a SATA SSD can work as well, as long as you don't expect the same performance.

If you have extra space on an internal SSD then you can install the other OS on a new container/partition there. More reliable than external SSDs and their vunerable USB/Thunderbolt cables.

You need to actually have access to the macOS/OS X installer. If you just want to go back to Mojave hopefully you have an installer saved or it's still available to you in the Apple Store. Go check on that now. If not you may need to go beg Apple Support for access.

If things were not working with Catalina you should be able to just roll back to your last clone/backup. If you are not making clones/backups start by getting that started now... backing up to multiple other removable drives.. and then you will need to also back up your new bootable external drive. Especially if you are new to this it's easy to totally screw yourself up when installing a new OS... get backups working before you start doing brain surgery.

If you want to roll back OS versions significantly you need to work out what the oldest version of OS X/macOS is supported on your iMac. There are multiple web sites that describe that. You cannot run older versions than the oldest version officially supported.

If you have a iMac Pro you have to do additional gymnastics to deal with the T2 security chip to allow booting off an external drive.

Last edited by Darryl Ramm; 02-01-2020 at 03:30 PM.
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