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Re: ext3 real disk occupation of a file

Hi Eric,

I have understood from the document, that for each file, we have 3 extra blocks (indirect) that refer to  :

- the group descriptor
- the block bitmap
- the inode bitmap

Is that right?

If not, to what the indirect blocks refer to? and are there always only 3 blocks for each file in ext2/3fs?

Best regards


On Tue, Aug 18, 2009 at 4:45 PM, Eric Sandeen <sandeen redhat com> wrote:
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:
in that paper.


> Thanks for help!
> youness
> --


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