Today I got my machine locked up (in the sense that (shell/GUI) programs cannot be closed, but the mouse cursor still moves). This happened while I was fiddling with IPv6 tunnels, iptables rules and related stuff. Luckily, I had a journalctl open so I could see that a BUG happened with something about nf (netfilter).
Since the machine was unusable, I issued REISUB. To my horrible surprise, the recent entries were GONE from the log. Before systemd, syslog-ng always saved the logs even if it was garbled or duplicated/interleaved. Since journald works nicely for most purposes, I want to keep it as the main logging daemon. But for kernel messages (dmesg), I want to have it written to disk immediately before systemd loses it (not necessary synced, S from REISUB should sync as needed).