From the A310 FCOM: 1-10.50 Flight Instruments
Primary source for IVSI is the IRS. An auto switchover to ADC input occurs if there is a problem with the IRS
Normal Ops: VSI repeats the IVSI data from the IRS, filtered by ADC info for stabilization
If IRS input lost - switched automatically to ADC input only (->slow response like standard VSI)
If ADC input lost the VSI will operate BUT ONLY FOR 30 SECONDS! then the OFF flag appears and the pointer returns to Zero
so I guess everybody is right
