i found answer to my question after did some R&D on glusterfs, There is no way you can point gluster to other log file without restarting it. truncate is a good option to reduce the log file file size if space is the issue.
regarding what would happen if i restart the glusterfs service answer to that is nothing would happen to it because glusterfs is configured in distributed replication mode. and there are 2 servers in replication with 4 bricks on them 2 each. if you restart the glusterd daemon on one server i wont effect the real time db, glusterfs provide real time fail over. when you deamon comes online it starts auto healing.