I've got this complicated backup routine with my photos that gives me confidence that I have 2-4 copies of each photo. There's the one on the camera (at first), the primary one on the server that files are copied to but never overwritten. Then there is an auto copy to another drive of the entire folder, which does overwrite. Then there is a manual move (not a copy) to a third drive than contains a tiered copy to a block segmented folder which is then diffed with TwinSeek (using auto delete) with the hope that all the previous files are found to match the ones from the new folder. By this stage the camera is generally removed to a separate folder on the primary file server and after one of the auto copies TwinSeek is used to ensure that these files are already on the server. Eventually all the photos are copied to archive drives in a fireproof safe. (Untested.) Thus, if you do the maths, I end up with 2-4 copies most of the time.
This requires me to have extra space on my backup drives to cover the extra doubles that are there prior to the difference check. However... I recently came back from a 5 months trip with around 1 TB of photos and thus the system is not really working. Sigh. It's been a lot more manual and takes more steps to make it kinda progress. Long term I'll probably move the tiered copy to a bigger drive as that will always need to have preferably at least 50% more than they space backed up so the diff takes two passes. But at this point in time I'm not even sure what size I even need...
Moral of the story; pre-capture. It's cool but dangerous. I have a policy of don't-delete-any-photos, but I might be changing my mind soon...
