2nd internal hdd SATA3 fstab MBR vs GPT

Before running up against the wall, I may ask if someone has got a clue how to mount a second internal hdd. gpart shows me the following

=>  34  976773101  ada0  GPT  (466G)
  34  2048  1  bios-boot  (1.0M)
  2082  6  - free -  (3.0K)
  2088  972558336  2  freebsd-zfs  (464G)
  972560424  4194304  3  freebsd-swap  (2.0G)
  976754728  18407  - free -  (9.0M)

=>  63  1953525105  ada1  MBR  (932G)
  63  2016  - free -  (1.0M)
  2079  1953521577  1  freebsd  (932G)
  1953523656  1512  - free -  (756K)

=>  0  1953521577  ada1s1  BSD  (932G)
  0  1953521577  - free -  (932G)

all the other commands do well, such like

gpart list
gpart status
diskinfo -ctv ada1
but as soon as I even try to add a line as root to
I am thrown back at the emergency boot via console.
Here is the line I added to fstab
 /dev/ada1 /newdisk zfs rw 2 2
but this very entry causes me quite a headache. Even trying to change the MBR to be GPT did not work.
So someone knows how to solve this riddle? Thanks in advance.
I will try this, it can only get better, thanks. I referred to https://www.freebsd.org/doc/handbook/disks-adding.html

So following the instructions given on the site mentioned above I see now
typing as root in the terminal
newdisk  942669644  96 942669548  0%  /newdisk

One test I made before, which resulted in reinstalling the system, I removed sudo from
Not removing sudo and after adding a line to
Here is the line I added to fstab
 /dev/ada1p1 /newdisk zfs rw 2 2
Adding a line now to fstab and rebooting shows me, all remains the same. As if sudo is fooling me. Removing sudo freezes at rebooting. Mounting or entering the folder /newdisk results in nothing.
# mount /newdisk
mount: /dev/ada1p1: No such file or directory
So I found the only hint in some peculiar code like the following
ada1 at ahcich1 bus 0 scbus 1 target 0 lun 0
May someone can help me out, thanks in advance!
The first disk, the boot-disk is a raid 0, I am aware of this. The second should act only as a mass storage.
Forget about /etc/fstab if you want to use ZFS. You'll also want to remove that slice.

gpart destroy -f ada1 # make absolutely sure you have the correct disk!
zpool create mypool disk /dev/ada1