A wedding, graduation or family portrait cannot always be repeated. When your camera supports it, recording each image on two cards creates an additional copy at the time of capture. But both cards remain in the same camera: loss, theft or damage can affect them together. This setup therefore does not replace backups outside the camera.
Three settings that serve different purposes
- Backup or simultaneous recording: each photo is written to both cards.
- Overflow or relay: the second takes over when the first is full; this increases available capacity, not the number of copies of each image.
- RAW on one card, JPEG on the other: you split the formats. The second card does not necessarily contain a second RAW file.
These distinctions are described in the Nikon Z 8 manual, secondary slot function. On this model, behaviour also depends on the image quality selected; in RAW + JPEG mode, the split separates these two formats. This is a documentation example, not equipment declared as belonging to Tim.
Photo and video: check separately
In the same manual, Nikon refers video to the “Destination” setting in the video menu. Do not assume that the photo backup mode duplicates movies. For your camera, check the exact video mode, format, resolution, frame rate and compatible cards in its documentation, then run a test before filming.
The right question is not just “does my camera have two slots?”, but “which files do I actually get on each with my settings?”. A greyed-out option or a warning must not be ignored just to get started faster.
A practical check before a session
- With compatible cards and free space available, select the desired mode using your camera's manual. Do not format a card containing files that have not been backed up.
- Take a few easily recognisable test photos. For video, also record a short clip with the planned settings.
- Wait until writing is complete, then follow the manufacturer's procedure for switching off and removing the cards.
- Read each card separately on the computer. Compare the names, formats and resulting files; open images and the clip rather than relying solely on the number of folders.
- Note the verified setting and repeat the check after a significant configuration change.
This test checks your configuration at the time of testing. It does not prove that a card will never fail. Do not cause a write error by removing a card during recording.
After the session: get copies out of the camera
The principle 3-2-1 described by Backblaze means keeping three copies of the data on two types of media, with one off-site. The working copy counts as one of the three. Geographic separation notably reduces the risk of a single incident destroying all copies.
Prepare a clearly named session folder, copy the originals and check that the backup is complete before reusing the cards. Also run a small restore test into a separate folder. Keeping files without knowing how to recover them does not meet the need.
Only have one slot? Still arrange copies outside the camera as soon as possible and prepare the storage media before the session. No setting can add a second physical card. Avoid turning every break into hurried handling, though: a simple, checked and repeatable process is better.
Preparing images and their future
File security is part of planning, just like the location and schedule. For a professional project, continue with our guide to preparing a team photo session. And if you would like to understand your own camera's menus, the TimFocus photography courses offer a way to address your practical needs.
Written by TimFocus. Nikon and Backblaze documentation accessed on 16 October 2026. No failure rate, personal test, equipment belonging to Tim or guaranteed result is claimed.