Bit rot

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Barugon Veteran Member • Posts: 8,974
Bit rot

I was reading Fstoppers and came across this article about bit rot. The author has the notion that his images, once written to a digital medium, will degrade over time. He has some pretty big misconceptions here.

It's true that all digital storage can only be written to some (very large) number of times and that applies to the individual bits (however blocks of data are written at once), not the whole volume. Many newer technologies, like SSds, employ a rotation mechanism for writing data. That is, it will write to a specific location but it won't write to that location again (provided that location is marked as available) until it has gone through all the available storage locations. Once it has gone all the way around then it will write to that location again. This helps distribute the wear and greatly increases the longevity of storage devices.

Keep in mind that once you write a file to some storage medium then it stays put and that location is not written to again. You can read from an SSD, SD or other digital storage any number of times without degradation. All electronic devices can still ultimately fail so it's still a good idea to maintain more than one backup or consider using DVD or Blu-ray.

The article above suggests archiving your images on film. To me, this is an insane solution to the problem of potential data errors. I suggest using a data recovery format like par2 or rav when you write your images to a backup. The rav recovery file format is available via WinRAR but I personally use par2 as it's open source (I also use Linux). Here's how it works.

Create a recovery:

par2 c -n1 PS5_0087.RW2

The -n1 parameter tells it put all the recovery information in one file. The par recovery format was invented when people used the highly unreliable usenet for sharing files, so par2 will split the recovery data into multiple smaller files so that if one or two are missing it can still repair the original file.

To verify a file run:

par2 v PS5_0087.RW2

This will probably tell you "All files are correct, repair is not required." However, if you do need to repair the file then run:

par2 r PS5_0087.RW2

This, to me, is a much better way to ensure the integrity of your images.

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