A Peculiar Blog

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It occurred to me that in my quickie freenet tutorial I mentioned, but didn’t really do a very good job of explaining the concept of "Healing" files that you download. I found the following explanation in a frost posting by "sparhawk" that explains it much better.

When you insert anything into Freenet from any program, it gets split into blocks with Forward Error Correction (FEC) of 33% added. Therefore, if you insert a 100MB file, 133MB really get inserted, and any downloader only needs to retrieve 75% of the blocks from the 133MB to stitch back the original file.

"Healing" means that you will re-insert blocks from that file back into the network to keep the file alive. Over time blocks fall off the network — either because they are unpopular or because a node goes down or a hard-drive crashes somewhere (which is probably always happening given the size of the network) — so healing is a nice thing you can do to keep that file retrievable for other people. Healing will also first re-insert all of the blocks that you couldn’t retrieve. So at a minimum, it is nice to set healing to 25% to put back all of the blocks that you yourself couldn’t get.

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