33 MB used on a empty partition?

[Joao Clemente <jpcl@rnl.ist.utl.pt>]

Hi. I was running some system checks on a server where I had created a 
partition for future use...
This partition has 60GB, formatted with ext3 with largefile option 
(created with the sarge debian installer) and the only thing I can see 
there is the "lost+found" folder...

df shows
jpcl@linux:~$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
...
/dev/md5              58875084     32828  55897952   1% /backup

or, using this output to be more visible
jpcl@linux:~$ df -h
Filesystem            Size  Used Avail Use% Mounted on
...
/dev/md5               57G   33M   54G   1% /backup


However, du shows:
linux:/home/jpcl# du -sh /backup/
20K     /backup/

...

So, where are those 33MB going to? Is it related to "largefile"? Or 
maybe by being ext3 (maybe the journal size)?
What tool can I use to find out the filesystem details? The partition 
sizes we can find out with fdisk, cfdisk, or whatever... but how do we 
check the "what filesystem, what blocksize, what journal size", ...?

Thanks
Joao Clemente