APFS compatibility with MacOS Extended (case sensitive journaled) and Installing Big Sir to replace Mojave.

TrickL wrote:

I have a 2013 macbook pro 15" I want to upgrade from it's Mojave, to Big Sur. It's internal SSD is formated to macOSExtended (case sensitive journaled)

The case sensitive file system may cause you problems when transferring files to a case insensitive file system since you may find some files will be marked as duplicates due to having the same characters in the file name, but with a different case (upper or lower). Most people should never use a case sensitive file system on the main boot drive, and people should be very careful when they do so on a secondary drive. Usually the only people needing a case sensitive file system are developers who create software for multiple operating systems (especially Linux).

I'm toataly new to mac. and if I wipe and reformat my main drive to install the new OS and sometihng crashes. I don't want be left with a useless brick. I would greatly apreceate some help understanding this. Thanks .. Patrick L.

Create a bootable macOS Big Sur USB installer using the instructions in this Apple article:

Create a bootable installer for macOS - Apple Support

Edit: Theoretically you should be able to convert the HFS+ file system to APFS without erasing the drive & without losing any data. However, there is always a chance something may go wrong, so make sure to have a good backup first. Also, some people have reported that Disk Utility won't always convert the file system and unfortunately the Big Sur installer no longer performs the conversion automatically IIRC. I'm not sure how it will work since you are using a case sensitive file system. You will need to be booted to Recovery Mode, or Internet Recovery Mode, or from a bootable macOS USB installer (or from an external macOS with full OS). See this post by @tbirdvet:

CONVERTING TO APFS - Apple Community

FYI, people should always have frequent and regular backups of their computer and all external media (including the cloud) which contains important & unique data. Many times it is impossible to recover data from an SSD. There are a lot more new ways to permanently lose access to your data with a computer with the newer Macs due to all the hardware, software, and security features.

I wouldn't convert it yet, I'd format the external to APFS, then use CCC to clone the internal to the external drive, test booting from the clone, then if satisfactory you can Erase the Internal drive to APFS...

Carbon Copy Cloner seems to accomplish it...

http://www.bombich.com/software/ccc.html