Quick cheat sheet for mirroring a port to a span port:

rs@woodburn-bigswitch> show configuration ethernet-switching-options 
analyzer spanport {
    ratio 1;
    input {
        ingress {
            interface ge-0/0/0.0;
        }
        egress {
            interface ge-0/0/0.0;
        }
    }
    output {
        interface {
            ge-0/0/1.0;
        }
    }
}

rs@woodburn-bigswitch> 

and for mirroring all ingress traffic to a vlan to a span port:

rs@woodburn-bigswitch> show configuration ethernet-switching-options
analyzer spanport {
    ratio 1;
    input {
        ingress {
            vlan woodburn;
        }
    }
    output {
        interface {
            ge-0/0/1.0;
        }
    }
}

rs@woodburn-bigswitch>

This was done on an EX3200 but I’m sure it will work on other EX models as well.

Note that if you mirror a trunk port you’ll get 802.1q tagged traffic out the span port, while if you mirror a vlan you will get untagged traffic.