Hi Thangaraj,
I think 1Gbit can be used for VSF. In the past this didn't work but since the latest firmware release (WC.16.04.0010) it should. I haven't test this myself.
Copy from the release notes.
VSF CR_0000238068
Symptom: The switch fails to form a VSF stack when using a 1G connection for a VSF switch link.
Scenario: The switch fails to form the VSF stack when the VSF link is configured for a 1G interface. The standby switch reboot process triggered by the stack role election process hangs at "Initializing…"., while the commander switch reports a warning event log message similar to: I 01/01/90 00:04:00 03279 stacking: ST1-CMDR: Member 2 (941882-11c860) chosen as standby.Reason: Only available standby W 01/01/90 00:06:03 03838 chassis: ST1-CMDR: Co-Processor failed to boot. Timeout reached: System initialization failure
Workaround: Configure the VSF link on 10G interfaces.
Regards,
Willem