disk usage monitor figures don't add up?

[Jeff Vian]

On Thu, 2004-12-09 at 03:42 -0500, Gene Heskett wrote:
> Greetings;
> 
> I need a bit of help from the ext3 filesystem folks I think.   I'm
> haveing a comprehension problem here.  A snip from a df report:
> 
> /dev/hdd3      176100712   165509176   26340  100.3% /amandatapes
> 
> >From the above, there is about 10GB on the missing list!  Amanda just
> bailed out early because the disk was full, while the 2 figures on
> the left claimed there should have been somewhere between 10GB and
> 11GB of space left, not the 26 megs shown above.
> 
> The output of a du . on that partition, before I ran the amflush, was
> 165509176 bytes total used out of 176100712 that df claimed it has
> for a total, both in 1024 byte kilobytes.
> 
> So my question is: Where is the math broken?  Both du and df, or my
> head? 
> 
> Surely there cannot be 10+GB tied up in inodes and journals?
> 

Math is not broken.  The system automatically reserves a portion of the
partition that is usable only by root, and any user space application
will see the partition as 100% when it reaches this level. Without this
reserved space, when a partition becomes 100% full it would not even
accessible by root and thus the partition data could be lost completely.

IIRC the number used to be 10% reserved, 90% user back when drives were
a lot smaller. That may have changed but I do not know the actual number
now.

The available above and the difference in numbers indicate it still
might be the original 10% reserved space that got you.