02-05-2019 05:40 PM
For your wedding shooting with redundant recording to two cards I wouldn't bother with a backup to a portable drive at the event. The odds of both cards failing (or you losing both cards) is very small and you would have to weigh that against the possibility of making mistakes while trying to hurriedly make a backup during a short down time OR getting distracted and having the portable drive and cards walk away while you aren't paying attention during a transfer. I read on another forum about a photographer who was hurriedly transferring photos from his camera to a server and without thinking he chose his last used menu item on his second camera and instead of switching to communications he formatted the card instead. Bad things happen when you try to do something important during a short down time during a long event.
There are no guarantees but coming out of years of risk management consulting I would secure both cards when they come out of the camera and not do anything else with them until you are safely back at your own office.
Changing cards often and having a second camera in use is good insurance against unusual system glitches. A colleague who ran a product failure analysis firm told me several years ago about an event photographer who lost most of his material due to a camera failure that trashed both cards simultaneously and very little data was recoverable. Dual cards are good protection against the more common card failure but when things really go wrong, splitting the event between several groups of cards reduces the potential for large loss. You can drive the probability of image loss down to a very low level but you quickly reach the point where the cost of further decreasing risk increases at an extremely high rate and it isn't necessary (and certainly not practical) to drive risk to extremely low levels.
If you are doing a multi-day event away from your own turf, treat it differently and backup the files to another source and preferably a cloud at the end of each day. A good friend lost days worth of images, both the cards and the backup drive, from his hotel room near the end of a long trip.