[...]
logging {
	channel simple_log {
		file "/var/log/named/bind.log" versions 3 size 5m;
		severity warning;
		print-time yes;
		print-severity yes;
		print-category yes;
	};
	channel security_file {
		file "/var/log/named/security.log" versions 3 size 30m;
		severity dynamic;
		print-time yes;
	};
	category default {
		simple_log;
	};
	category security {
		security_file;
	};
};
[...]