Reverting to Mojave

[techbert]

Can a hard drive that was set up as APFS for Catalina, be returned to a file system compatible with Mojave?

 

[Lufbrarunner]

Mojave uses the APFS file system.
A clean install would be the best method.

 

[techbert]

I had thought that like El Capitan, Mojave used HPS+ file system.

 

[Lufbrarunner]

I have Mojave running and it is on APFS

 

[chrispl0]

Moved back to Mojave! Catalina just wouldn't work for me. crashes, destroyed 2 x 4TB external drives though constant crashes. Ill with it.

 

[Harry Trent]

APFS first appeared with the release of High Sierra but was optional, at least on a platter-based hard drive. With Mojave and later it is mandatory.

 

[valiant66]

I am booting from a fusion drive and an older OS. Will upgrading to Mojave convert that to APFS? And will that affect backing up to an external HFS+ formatted drive?

 

[Harry Trent]

Yes, the fusion drive would be converted to APFS. Beginning with Mojave, all system drives will be formatted with APFS, regardless of whether they are flash-based or platter-based. The Fusion drive, as you may know, combines those two elements into one unit. Using the drive utility you need to check and see if your backup drive has been converted to APFS. If it is not APFS I'm not at all sure it can be used to restore a system. Perhaps others with more in depth knowledge of how external backup storage works in the Apple world can give you a more definitive answer.

I do know that a Time Machine backup storage drive cannot be used to restore a system that has a later OS in place than was in use when Time Machine was first setup. To be safe, I would reformat the Time Machine backup drive (assuming here that you are using TM) in APFS and setup TM anew.

 

[Allen Davis]

54622-how-to-downgrade-from-macos-catalina-to-mojave-or-earlier

This article from Other World Computing should be a big help.