Ryan Pugatch wrote:
> Hi all,
>
> Curious issue.. looking in to how much disk space is being used on a
> machine (CentOS 5.3). When I compare the output of du vs df, I am
> seeing a 12GB difference with du saying 8G used and df saying 20G used.
>
> # du -hcx /
> 8.0G total
>
> # df -h /
> Filesystem Size Used Avail Use% Mounted on
> /dev/xvda3 22G 20G 637M 97% /
>
> I recognize that in most cases du and df are not going to report the
> same but I am concerned about having a 12GB disparity. Does anyone have
> any thoughts about this or reason as to why there is a big difference?
> I have read a few articles online about it and none have really shown
> such a large difference.
I see similar differences even when I:
a) Boot from a rescue CD,
b) Freshly fsck the file system to be tested,
and c) Mount that file system read-only.
I suspected the discrepancy might be due to the space used for the
ext3 journal, but I also see it on a freshly created ext2 file system:
# mount -r /dev/hda8 /mnt/tmp
# du -s /mnt/tmp; df /mnt/tmp
20 /mnt/tmp
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/hda8 13638436 33824 12911812 1% /mnt/tmp
So, there's a 33+MB difference on a fresh, empty ext2 file system.
Looking at the file system with debugfs, I find inode 7 is a regular
file of size 4299210752 and a block count of 67608. That's a huge
sparse file. A little research shows that this is the "resize inode"
that reserves space for future GDT blocks so that the file system can
be expanded in place.
--
Bob Nichols "NOSPAM" is really part of my email address.
Do NOT delete it.
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