Uploading very large file might not be reliable for all user anyway so doing slice would be a good idea. Obviously, you would need so code to ensure you got all slices (and that they are not corrupted) and resend missing or corrupted slices. In any case, you would not want to use default handling for such large files as it might take hours to upload a file and you would need to send some feedback to the user.
Jon Galloway - Large file uploads in ASP.NET[
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HTML Large File Uploader[
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You might also consider creating a standalone application to let your user send big files. You would then be able to give them better feedback on progress and maybe allows some tuning for best performance and possibly also implement pausing the upload and restart partial upload after a crash or reboot of the computer.