According to this guide I made the Journal persistent because I had a serious issue where I needed the logged information but it got lost after I reboot the server.

I would like to store the default Journal directory /var/log/journal/ on a mounted file system other than /, but I am not sure if I can do it due to the fact that Journal is an important service which may already run before any device is mounted which would lead to the fact that suddenly the directly changes.

Is it safe/possible to store the Journal directory on a mounted device and if yes, how to do it, if a simple mounting doesn't work.

This is the current directory listing which is getting bigger and bigger so there won't be enough space in few days on the / file system.
I have to create an additional virtual disk I use for the Journal file system.

2019-03-18 22:16:41 root@AAEB-APP206LY:/var/log/journal/d41cf15550e34487abe7103b61fbf794 => ll
total 792M
drwxr-sr-x  1 root systemd-journal  884 Mar 12 06:35 ./
drwxr-sr-x  1 root systemd-journal   64 Feb 26 18:17 ../
-rw-r-----  1 root systemd-journal  96M Mar 18 22:16 system.journal
-rw-r-----  1 root root            120M Feb 26 18:17 system@d5301574c947425cb992f7839ae52cdb-0000000000000001-0005827c7effc14d.journal
-rw-r-----  1 root systemd-journal  96M Mar  5 12:29 system@d5301574c947425cb992f7839ae52cdb-0000000000051acb-000582cf3a7ba719.journal
-rw-r-----  1 root systemd-journal  96M Mar 12 06:35 system@d5301574c947425cb992f7839ae52cdb-00000000000872b4-000583572e31154d.journal
-rw-r-----+ 1 root systemd-journal 128M Mar 18 22:16 user-5000.journal
-rw-r-----+ 1 root root            128M Mar  5 12:29 user-5000@cf6acecdf28e48c790173a36447ec2e7-0000000000051ad9-000582cf3d435013.journal
-rw-r-----+ 1 root systemd-journal 128M Mar 12 06:35 user-5000@cf6acecdf28e48c790173a36447ec2e7-00000000000872b9-000583572e312040.journal