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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

youness

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:
http://e2fsprogs.sourceforge.net/ext2-inode.gif
in that paper.

-Eric

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




--
Y.

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