Someone

mount {
        blkio = /sys/fs/cgroup/blkio;
}

group high {
        blkio {
                blkio.weight = "1000";
        }
}

group medium {
        blkio {
                blkio.weight = "500";
        }
}

group low {
        blkio {
                blkio.weight = "100";
        }
}