May the moderator should move this thread to BSD, because it did not work at all an linux.
I set in on the mountpoint /dev/usr and after rebooting the boot-routine told me, that the second hdd was not unmounted correctly.
Systemd forced a fsck for the 2nd hdd and after not even half of the 2nd volume I was stuck on a black screen with a cursor.

On linux it did not work at all. I guess even trying to replace systemd is quite a task, not to disturb the runnig system. So on linux with systemd for the enthusiasts of their distro they may try the following commands one after another and have a look at it.

Code:

systemd-analyze
systemd-analyze blame 
systemd-analyze critical-chain 
systemd-analyze dot | dot -Tsvg > systemd.svg
systemd-analyze plot > bootplot.svg

So I am fighting my way through bsd where to mount that hdd properly in the fstab. Here is the actual output of my fstab on bsd.

Code:

# Device                Mountpoint            FStype        Options    Dump Pass
/dev/label/swap0.eli    none                swap        sw        0     0
procfs                    /proc                procfs        rw        0    0
linprocfs                /compat/linux/proc    linprocfs    rw        0    0

This is interesting, pluggin the hdd into the bsd machine it is recognized by gpart list, but not yet ready to be accessed. After
typing

Code:

pkg install fusefs-ext4fuse

there are two entries in the drop down menu for the same device. As far as I know ext2 is the basic for cooperation between linux and bsd. So now I do not have the rights, because this device has been installed in another machine with another root and user. So what can I do? Something like

Code:

chmod -R 777 ada1

yes, I remember one user on this forum telling me, that this is not the magical sledgehammer, but I need the data of the disk, it is about some years of work. And since I am working on my own machine as a single user, whats the matter with that?

this is what

Code:

gpart list

tells me about the second hdd.

Code:

Geom name: ada1
modified: false
state: OK
fwheads: 16
fwsectors: 63
last: 1953525167
first: 63
entries: 4
scheme: MBR
Providers:
1. Name: ada1s1
   Mediasize: 1000203091968 (932G)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r0w0e0
   rawtype: 142
   length: 1000203091968
   offset: 1048576
   type: linux-lvm
   index: 1
   end: 1953523711
   start: 2048
Consumers:
1. Name: ada1
   Mediasize: 1000204886016 (932G)
   Sectorsize: 512
   Stripesize: 4096
   Stripeoffset: 0
   Mode: r0w0e0

So any hints to solve this problem? Many thanks in advance.