ext3 real disk occupation of a file

[Eric Sandeen]

Youness HAFFANE wrote:
> 
> Hi,
> 
> I'm trying to understand why extra blocks are added when you create a
> file in the ext3 fs:
> 
> for example, let's create a file of 1111 blocks (4096 bytes for each block)
> 
> $ dd if=/dev/zero of=foo bs=4096 count=1111
> 
> the real occupation disk is then:
> 
> $ du -B 4096 foo
> 1114
> 
> instead of 1111
> 
> So where the 3 extra blocks come from?

from the indirect blocks.  This is how ext2/3 keep track of the layout
of the file.

see http://e2fsprogs.sourceforge.net/ext2intro.html
and in particular the diagram:
http://e2fsprogs.sourceforge.net/ext2-inode.gif
in that paper.

-Eric

> Thanks for help!
> 
> youness
> 
> --