Fortunately our OLTP Database fits on one tape, we also restore to a backup database for immediate rollover in case of failure.
However recently we were hacked and although our DB was untouched some system files were corrupted so we could not load the DB.
We dump all our major files to csv files overnight from our OLTP DB and these were initially used as a psuedo Datawarehouse until we got our current full blown MS SQL version. Because these files were available we knew our customers addresses, we knew what stock we had, we knew where the stock was and we knew all the prices.
Now it wasn't as smooth and efficient as normal trading and the system says we didn't process anything that day but we got all the orders out that were due out. So the impact to the business was minimal and once the system files were restored all was well.
So how well you prepare for downtime is as important as getting the data back.