Ideally you should use backup software that does "versioning" or "Point in time recovery" (two of the common terms used). If you are not using backup software, but just copying files, it becomes harder.
Here's the mental test to do: Assume you had an image and replaced it with garbage of the same name today, but did not notice for 6 months. Would your backups have a copy that was 6+ months old so you could recover it?
The problem for most photographers is that they have years worth of images they may either never look at again, or look at very rarely. If something happens -- whether by human error or software problems or hardware problems -- we might not find out quickly at all. There are a few things one can do to sound alarms more quickly:
- With regard to the lightroom catalog, running the optimize and check feature with some regularity gives you a heads up on it.
- If you are using DNG's, there is a "Validate DNG files" option you can use, which checks the integrity of the image data inside the DNG (but not the metadata unfortunately). (Unfortunately there is no built-in option for raw, jpg, tiff, etc.)
- Periodically run the Find MIssing Files in Lightroom, to make sure whole files have no disappeared.
- Many people find programs, commercial or open source, sometimes integrated with their backup programs, which will take checksums of all files, save them somewhere, then do the same again and again -- it gives you a head's up if a file has changed that you did not expect to change (e.g. raw). This is useful even beyond Lightroom, for any kind of files you expect to sit on disk and not change to sound an alarm if they do change.
The reality is that most of the time our hardware is good enough, and software reliable enough, that absent a total failure files do not get corrupted. But equally real is that once in a while it does, and being prepared is a good thing.
