writing large files quickly

[Jens Theisen]

Donn wrote:

> Because it isn't really writing the zeros.   You can make these
> files all day long and not run out of disk space, because this
> kind of file doesn't take very many blocks.   The blocks that
> were never written are virtual blocks, inasmuch as read() at
> that location will cause the filesystem to return a block of NULs.

Are you sure that's not just a case of asynchronous writing that can be  
done in a particularly efficient way? df quite clearly tells me that I'm  
running out of disk space on my ext2fs linux when I dump it full of  
zeroes.

Jens