Thanks for your answer. It tells me that the observed behaviour is usual 
- no matter that I think it should not be usual. ;)

Am 30.11.2020 10:27 schrieb antlists:

quoted

Why is the system so sensible about one RAID device that does not 
contain essential data for the boot process. I would I understand if 
there is a error messages somewhere. But blocking the whole boot 
process is to much in my understanding.

It's not. It's sensitive to the fact that ANY disk is missing.

But the system does not need this disc to boot or to run. This IMO 
should not happen.

When a component of a raid disappears without warning, the raid will
refuse to assemble properly on next boot. You need to get at a command
line and force-assemble it.

This is logical to me.

quoted

quoted

sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
/dev/sda1 on / type ext4 (rw,relatime,errors=remount-ro)
/dev/md127 on /Daten type ext4 (rw,relatime)

And here is at least part of your problem. If the mount fails, systemd
will halt and chuck you into a recovery console.

btw: I am not able to open the recovery console. I am not able to enter 
the shell.
In the Unix/Linux world all things have reasons - no matter that I do 
not know or understand all of them.
But this is systemd. ;)

I see no no reason to stop the boot process just because a unneeded 
data-only partition/drive is not available.

Is root's home on /Daten? It shouldn't be.

No it is not. As you can see in the second line of the fstab / (and all 
its sub-content like home-dirs, boot, etc) is on /dev/sda1. The RAID is 
build of sdb and sdc.