Making apps use the fallocate() syscall instead of writing zeros to a file is the preferred way to init a file with all 0s. I was pleasantly surprised ktorrent already does that (but via a non-default config option):
I would like it if they made posix_fallocate() the default, if available on the target system. posix_fallocate() already uses fallocate() if supported by the filesystem, otherwise it falls down to the writing zeros block-by-block method. My last post showed the comparison of various file allocation methods, the performance of filesystems and also the fragmentation each method causes.
Reading that post again, it looks like it could've been written much better and could've used a couple of editing rounds. So I've decided to do a second post which will have better results and more file systems added to the fray. I've updated the test to calculate the numbers more reliably and have also run the tests once more with more filesystems and taking factors like hard disk geometry, seek times, etc., out of the equation. The git tree is already updated with the new code, so you can try it out yourself. In any case, stay tuned for the results.