Well I have put up a stream for Fedora Core 3, and it is on the streams page. I am disappointed with the results though: only a 20% saving on the total download (starting from Fedora Core 3 test3). Perhaps I need to tune the blocksize, or do something else to optimise for iso9660 filesystems.

Anyway, some people might be interested in another trick, which is to combine zsync with bittorrent. First, use zsync -i FC3-test3-i386-disc1.iso http://zsync.moria.org.uk/s/FC3/FC3-i386-disc1.iso.zsync to start a zsync download of FC3 using data from the test3 ISO. As soon as it reaches the downloading from stage, ctrl-c it. Then start a bittorrent download, and exit after bittorrent has begun to download. Then copy the get.part file over the FC3-i386-disc1.iso.zsync that bittorrent has started. And restart bittorrent. Bittorrent should think for a bit, and then show the file as 20% completed or so. It will then fetch the rest of the file via bittorrent — and will even upload chunks of the file from the zsync'd results. Uploading from a file you've never downloaded, now that's a bit scary :-).