Fast and efficient updater

I'm developing an updater for a game client, so that the players won't have to download the whole client when it gets updated.

Now, creating a standard updater isn't really hard, but it's quite slow with large files.

The client is about 1,5 GB uncompressed and has ~250 files. The files on the update server are gzip-compressed and get downloaded via HTTP.

The updater works like this: get patchlist from server -> compare files from patchlist with local files (crc32 / filesize) -> if missing/wrong filesize/hash is not the same -> download gzip compressed file from server -> decompress file

The most time consuming parts of the updater: generating crc32 hashes for every file / downloading big files

I've thought of some things that could speed it up:

• Rsync-like diff updater - This would speed up the download, because it would only get the different part of the file and not just download the whole file. This would be helpful because usually a client update doesn't affect many parts of big files. But I guess it would be some kind of overkill for this purpose.

• Better compression - Gzip saves about ~200 MB when the client gets compressed. I haven't tried using some other compression methods, but I guess bzip2, lzma or else would save more space and speed up downloads. Ironically they would slow down the decompression of the files.

• Other file-check method - At the moment I'm using a C# crc32 implementation, because it was faster than standard c# md5 implementation. Are there any faster algorithms which can tell if a file is the same?

• Version system - It wouldn't actually speed up anything, but the updater wouldn't have to calculate all hashes. And with an additional "repair"-function it could just check all files against the actual version, if the user wants to.

Which of these solutions should I be using, or are there any approaches that I haven't listed that I should be using instead?