Ext3 users - May 2006 - Why different directory sizes?

I just discovered two directories with the same number of files and the same 
number of hard links but different size:

# stat /home/david/linuxburg/fax.old/docq_ps.nnnn \
       /hdsync/home/david/linuxburg/fax.old/docq_ps.nnnn
  File: `/home/david/linuxburg/fax.old/docq_ps.nnnn'
  Size: 8192            Blocks: 16         IO Block: 4096   directory
Device: 801h/2049d      Inode: 52060       Links: 2
Access: (0775/drwxrwxr-x)  Uid: ( 1000/   david)   Gid: (  100/   users)
Access: 2006-01-30 04:15:15.000000000 +0100
Modify: 2006-01-16 19:33:28.000000000 +0100
Change: 2006-01-16 19:33:28.000000000 +0100
  File: `/hdsync/home/david/linuxburg/fax.old/docq_ps.nnnn'
  Size: 16384           Blocks: 32         IO Block: 4096   directory
Device: 811h/2065d      Inode: 1128588     Links: 2
Access: (0775/drwxrwxr-x)  Uid: ( 1000/   david)   Gid: (  100/   users)
Access: 2006-03-11 16:45:25.000000000 +0100
Modify: 2006-01-16 19:33:28.000000000 +0100
Change: 2006-01-23 02:03:57.000000000 +0100

The file systems are identical, except that one is mounted "ro":

# mount | grep -E '/hdsync/home |/home '
/dev/sda1 on /home type ext3 (rw,noatime,nodiratime,acl,user_xattr)
/dev/sdb1 on /hdsync/home type ext3 (ro,noatime,nodiratime,acl,user_xattr)

The kernel is a standard SuSE 9.2 one:

# uname -a
Linux pserver 2.6.8-24.14-default #1 Tue Mar 29 09:27:43 UTC 2005 i686 athlon 
i386 GNU/Linux

What could be the reason for the different sizes?  They confuse our backup 
script.

-- 
Dipl.-Phys. Felix E. Klee
Email: fk at linuxburg.de (work), felix.klee at inka.de (home)
Tel: +49 721 8307937, Fax: +49 721 8307936
Linuxburg, Goethestr. 15a, 76135 Karlsruhe, Germany

Forgot something, namely the number of files in each dir:

# ls -l /hdsync/home/david/linuxburg/fax.old/docq_ps.nnnn | wc -l
209
# ls -l /home/david/linuxburg/fax.old/docq_ps.nnnn | wc -l
209

They're identical, as mentioned in my previous message.

-- 
Dipl.-Phys. Felix E. Klee
Email: fk at linuxburg.de (work), felix.klee at inka.de (home)
Tel: +49 721 8307937, Fax: +49 721 8307936
Linuxburg, Goethestr. 15a, 76135 Karlsruhe, Germany

On Wed, May 10, 2006 at 12:35:36PM +0200, Felix E. Klee
wrote:
> I just discovered two directories with the same number of files and the
same
> number of hard links but different size:
>
> What could be the reason for the different sizes?  They confuse our backup 
> script.
The reason is history.  Like many Unix filesystems, ext3 doesn't
garbage collect empty blocks in a directory.  So if you create a lot
of files in a directory, and then delete them all, the directory
doesn't shrink in size.  In practice this isn't a problem, so we've
never bothered to fix it.  

Why should your backup script care?  It really shouldn't....

						 - Ted