I was lucky so I better write it down.
Linux sucks. I'm using Ubuntu 20.04 and it wouldn't boot any longer. Recovery console was too fast to catch so I booted with an installation USB.
Then the question is: how to mount my old hard disk and copy my /home/data to safety!
sudo su -
mkdir /home/myhome
zpool status
sudo zpool import rpool rpoolssd
--> you have to rename rpool to avoid conflicts, or so I think!
zpool status
Which gives for me:
pool: bpool
state: ONLINE
scan: scrub repaired 0B in 0 days 00:00:01 with 0 errors on Sat Aug 7 22:24:03 2021
config:
NAME STATE READ WRITE CKSUM
bpool ONLINE 0 0 0
c2124c91-6e47-ff42-85e7-3c1199be6f2b ONLINE 0 0 0
errors: No known data errors
pool: rpoolssd
state: ONLINE
scan: scrub repaired 0B in 0 days 01:52:25 with 0 errors on Sun Aug 8 00:16:27 2021
config:
NAME STATE READ WRITE CKSUM
rpoolssd ONLINE 0 0 0
c6576671-0ca6-f14a-9633-088e41e229d4 ONLINE 0 0 0
zfs list -ro canmount,mountpoint,mounted,name rpoolssd
--> that gives, for me:
on /home/myhome no rpoolssd/USERDATA/myhome_a3k59c
on /root no rpoolssd/USERDATA/root_a3k59c
zfs set mountpoint=legacy rpoolssd
mount -t zfs rpoolssd/USERDATA/myhome_a3k59c /home/myhome