Recent version of macOS have actually been especially tough difficulties for the system installer. Very first we have actually the proceeding need to transform startup quantities from HFS+ to APFS, which has actually been mandatory because Mojave, also if her Mac usually boots indigenous a difficult disk or combination Drive. Climate Catalina has actually to split earlier single boot volumes right into its brand-new Volume team format, make a different read-only system volume and leaving every the users’ records on the connected Data volume.

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There room two simple situations for the installer to deal with with: upgrading native Mojave or previously with a solitary boot volume, and a vanilla re-install.

In the first case, the installer take away the present boot volume, through default called Macintosh HD, renames the Macintosh HD - Data, and also removes most of the device folders and files. It climate creates a new volume called Macintosh HD, onto which the installs the an excellent majority of the device files, and also which it makes read-only and also protects with SIP. The 2 volumes likewise need assorted stitching with each other points in unique firmlinks, which must also be produced during the installation.

In the 2nd case, the installer have to take an present Volume Group, and simply re-install every the system papers without mental the volumes and also their linkage.

The installer has to be smarter when taking care of clean re-installs, and also their variations. Apple has proposed a scheme by which clean installs must be came before by the user deleting the present Data volume and erasing the system volume. Yet in numerous (perhaps all) cases, this doesn’t in reality work, at least in version of Catalina increase to and also including 10.15.2. Once the user tries to erase the current System volume in regional Recovery mode, the operation fails because:The volume "Macintosh HD" on disk2s5 couldn"t it is in unmounted due to the fact that it is in usage by the procedure 734 (kextcache)

If you disregard that error and also press on through trying to re-install Catalina, the installer refuses, reporting that “The target volume is part of an incomplete system and also cannot be set up to.”


The only way to erase your mechanism volume is to restart right into Recovery mode and shot to erase it again utilizing Disk Utility, repeating this cycle of restart-erase until you are finally successful. Only then, with the device volume completely erased, will the installer have the ability to proceed.

Why, though, have to the user take it a perfectly good Volume Group, have to break the apart, delete their whole Data volume, and also then beat Russian roulette trying to erase their system volume, every to perform a clean re-install? It should be sufficient simply come erase the Data volume and also then continue with the re-install. The Catalina installer requirements to give users the flexibility to decide what of your existing macOS environment they want to delete before re-installing. In ~ present, if friend depart in any way from this facility procedure, the installer reportedly cannot cope.

I doubt one reason for present inflexibility is the system for creating the firmlinks on i m sorry this Volume team scheme depends, i m sorry Apple doesn’t document. If you just erase the Data volume, the firmlinks there will be removed, and also perhaps the installer is can not to replace them as soon as it tries to rebuild that volume’s structure. If that’s the case, it bodes ill because that firmlinks: one factor for wanting come re-install macOS would be damage to one of the firmlinks. If the only method to accomplish that is to delete that whole volume, that’s negative news because that the user.

The installer’s present behaviour v existing Volume teams seems bizarre. When offered an intact Volume group with an erased Data volume, the installer:

breaks the Volume group by removed the Data volume native it,creates a new Data volume through a name obtained from the currently Data volume rather than its equivalent System volume,makes a brand-new Volume group containing the original mechanism volume and the newly developed Data volume,installs editable system files, firmlinks, etc., ~ above the brand-new Data volume.

This is counter-intuitive, undocumented, and also worryingly common: most likely the most frequently reported error once installing Catalina is the creation of duplicate Data volumes, and also some users have encountered not just Macintosh HD - Data - Data however the absurd Macintosh HD - Data - Data - Data, every of which needs to be deleted once trying to rectify these troubles in recovery mode.


Is it really past the capacity of an installer to recognise an existing Volume Group and also to usage its constituent quantities as the location for the installation? If you room performing that re-install since of suspected damages to either volume in the group, can the installer cope with that, or is this intricate clean re-install the just robust technique of fixing troubles in her Catalina installation? Is Catalina really the fragile?

I have updated my current article about clean re-installs in Catalina in the light of this unpleasant experience. If you try to follow Apple’s present instructions, be conscious of the following issue:If an error is returned as soon as trying come erase the mechanism volume, any attempt to re-install macOS will fail. You have to restart ago into Recovery mode and try to erase the mechanism volume again, repeating that until successful. Only when the mechanism volume has been efficiently erased, and the Data volume has been deleted, will you be able to re-install macOS.

The end result is that, in Catalina up to and including 10.15.2, clean re-installing macOS is a fragile process which can fail, and also must be brought out to the letter. Any type of attempt come deviate will avoid the installation native occurring, and the user will be left floundering in Recovery setting with an unbootable system.

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I am really grateful to Ethan, my grandson, that tested the clean re-install procedure remotely ~ above his handed-down MacBook agree (non-T2), i beg your pardon isn’t a bad Christmas present.