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# Re: ext3 real disk occupation of a file

• From: Youness HAFFANE <youness254 gmail com>
• To: Eric Sandeen <sandeen redhat com>
• Cc: ext3-users redhat com
• Subject: Re: ext3 real disk occupation of a file
• Date: Tue, 18 Aug 2009 23:43:15 +0200

I see,
So for only the first 12 blocks, there is no need for extra blocks, but I couldn't find any mathematical logic for the rest.
I explain :
I've tried to create many files to which I assigned a fixed number of blocks, and the results are :
for a 13 block file till a 1036 block file I had 3 extra blocks added
and then it's 4 extra blocks added (for example a 3060 block file)
and for a 4000 block file, it's 5 extra blocks
for 5000 it's 6
and for 10 000 it's 11 blocks added!

so is there any logic?
or it depends on the machine (regardless if it is ext3, or another fs)?

Best regards

youness

On Tue, Aug 18, 2009 at 8:05 PM, Eric Sandeen wrote:
Youness HAFFANE wrote:
> 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?

nope :)

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

No.  basically the extra blocks are for keeping track of where the data
blocks are, or for keeping track of where more indirect blocks are,
which in turn keep track of where the data blocks are.

Maybe http://www.nongnu.org/ext2-doc/ext2.html#DEF-INODES has a better
explanation:

"There are pointers to the first 12 blocks which contain the file's data
in the inode. There is a pointer to an indirect block (which contains
pointers to the next set of blocks), a pointer to a doubly-indirect
block (which contains pointers to indirect blocks) and a pointer to a
trebly-indirect block (which contains pointers to doubly-indirect blocks). "

It's all these indirect blocks that you're seeing.

-Eric

--
Y.

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