Fedora Core 4 and FC5's NEW EXT3 file system: "Reserved GDT blocks" ???

[Robinson Tiemuqinke]

Hi,

 I've installed a few Fedora Core 4 and Fedora Core 5
recently, and found that the new ext3 file systems
created with new mkfs.ext3(1.38+) has one more field
than EXT3 created with old mkfs.ext3(1.34-), even the
latter's dir_index feature was turned on and file
systems were upgraded with "e2fsck -y -f -D" command.

 I have three questions thereafter:

1) what does the "Reserved GDT blocks" mean? and what
are its functions and purposes?

2) for file systems created with older versions of
mkfs.ext3(v1.34-) on FC1, how to upgrade it to the
newest version? 

I manually turned on dir_index(which is by default OFF
for 1.34-, but by default ON on 1.38+) with command
"tune2fs -O dir_index", then run command "e2fsck -y -f
-D" to upgrade it (e2fsck is 1.38+).

If the above upgrade way is the "official" way? If
not, then what is the prefered way to upgrade old ext3
file system to be used on FC4/FC5?

3) are there any other difference besides "Reserved
GDT blocks" between newly created ext3 file systems
and upgraded ones by e2fsck?

Please help. 

Thanks a lot.


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