@frollic and @VA1DER thank you very much for the information. I finally got working on it, and seem need some more help. I switch system log to the SD-card, but it seems system logging starts before SD-card is mounted (logically) and system log file does not appear on the SD-card. What would be the right procedure to switch log file to the removable location, or have it switched automatically when SD-card is mounted?
I am ok with the two-log-file configuration, adding logrotate would be the next step if system-provided logging mechanism will prove unsatisfactory.