Nico Dudek wrote:For this scenario
I need a backup strategy.
This is an excellent place to start.
Can I backup the FD completely on an external HFS+ disk?
With QRecall, yes!
QRecall chops up your files and stores that information in (essentially) a database. You're not actually storing the files or directories on the archive's volume, so the capabilities of the filesystem where the archive is written makes no difference. You can store APFS file on an HFS+ volume, HFS+ files on a Windows (FAT32) volume, ...
I guess not cause Catalina system requires an AFPS volume and AFPS on spinning HDs is endlessly slow.
Again, it doesn't matter. Also, APFS is much faster now. (In its early days, APFS was developed exclusively for SSDs and was not optimized for HDs, but that's in the past.) And going forwards, QRecall 3 will take advantage of APFS features for faster, and more reliable, archive updates.
So maybe one possibility is to backup only the data/document folder onto an external HFS+ disk and in case of a a drive failure
do a catalina system install from another SSD with APFS where I installed the system backup with all programs etc.
This is exactly what QRecall does now.
Starting in Catalina, your startup volume is actually two volumes. The system files are sequested on an immutable volume; a volume that cannot be modified, even by the kernel. The only[*] way to reinstall your operating system is to use the Apple macOS installer. When you capture your startup volume, QRecall find's its "data" volume (the secondary volume that you can write to) and captures everything there. The immutable system files are ignored.
To perform a whole-volume restore of a startup volume, you begin by formatting the volume and reinstalling the macOS (either via recovery mode or from an external startup drive -- I recommend creating a bootable USB drive for this purpose). Once installed, you can then use QRecall to restore the volume; QRecall will figure out that this is a startup volume, find the "data" half, and restore all of your files. Alternatively, you can then boot from the new system volume, reinstall QRecall, then use that to restore your files, but I prefer the former technique.
So here's my suggested preparation. Using either a handy external drive (which can also be the one your archive is stored on), or a bootable USB stick you keep around for emergencies:
Format the drive/stick APFS
Install a copy of Catalina
Reboot from the dirve/stick.
Download and install QRecall
Download and keep copy of the Catalina installer
When disaster strikes:
If replacing your drive, do the hardware swap.
Boot from the external drive/stick you created earlier.
Format your new startup drive and install macOS using Apple's installer.
Launch QRecall, open your archive, and restore the captured volume to the new one.
Reboot your new system and get back to work.
Does that make sense for you?
[*] Technically, you could restore the system files by booting from another volume and turning all of the safeties off, but I think that's a terrible idea and QRecall no longer supports this (without some hacking).