index directories in ext2 / ext3

Andreas Dilger adilger at
Mon Feb 8 21:47:54 UTC 2010

On 2010-02-08, at 13:59, Gaëtan Podevijn wrote:
> I am currently working on a little article. I would like to explain  
> the differences between ext2, ext3 and ext4.
> During my researches, I read that ext2's directories are implemented  
> with a linked-list structure. I also read Daniel Phillips's article  
> "A Directory index for ext2" (2002) and I'm a bit troubled.
> Indeed, I see that the HTree data structure was developed for ext2  
> but I cannot see anywhere that the current ext2 implementation uses  
> that data structure.

That is correct - it was developed for ext2, but since the new  
filesystem development was happening in ext3 the feature was landed  
only in ext3.

> Could you explain me why people talk about "index directories for  
> ext2" but there's no ext2 implementation that uses the HTree  
> structure ? Is it only for ext3 ? Since when ? Could you give me  
> some source that explain when was implemented HTree in ext{2,3} ?

Cheers, Andreas
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

More information about the Ext3-users mailing list