macbook pro volume could not be unmounted

In the second case, the installer should take an existing Volume Group, and simply re-install all the system files without disturbing the volumes and their linkage. The two volumes also need various stitching together points in special firmlinks, which must also be created during the installation. It then creates a new volume named Macintosh HD, onto which it installs the great majority of the system files, and which it makes read-only and protects with SIP. In the first case, the installer takes the current boot volume, by default named Macintosh HD, renames it Macintosh HD - Data, and removes most of the system folders and files. There are two simple situations for the installer to cope with: upgrading from Mojave or earlier with a single boot volume, and a vanilla re-install.

Then Catalina has to split earlier single boot volumes into its new Volume Group format, making a separate read-only System volume and leaving all the users’ files on the connected Data volume. First we have the continuing need to convert startup volumes from HFS+ to APFS, which has been mandatory since Mojave, even if your Mac normally boots from a hard disk or Fusion Drive. Recent versions of macOS have been exceptionally tough challenges for the system installer.

Macbook pro volume could not be unmounted