Heatmap | More contrast
(Black/blue parts are the unchanged blocks)
Here's a little fun data visualization.

This is a heatmap of a day worth of changes to a large TrueCrypt container file that was backed up with delta copying and all block changes diligently saved as a bitmap. Block changed - its bit is 1, unchanged - the bit is 0.

Container file is 256 GB, the block size is 64 KB, which gives us 4M of blocks to the total of 512 KB when packed into a bitmap.

With the bitmap at hand, we head over to binvis.io to generate a 2D entropy map using a Hilbert curve fill, overlay with absolute changes, then pass it through some cosmetic filters and, voilà - a simple way to see where the delta copying gets its speed from.

The brighter parts are the 10 Gigs worth of changes, the dark background is 246 GB of unchanged space... meaning that we ended up copying under 4% of the file and spent a fraction of time doing that.

*   For a detailed tour of delta copying see here.
Made by IO Bureau in Switzerland

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