strange dump (dark matter?)

[Ryan Sandridge]

Hello all.  I decided it was time to start doing backups.  On Oct 7th, 
I did a full dump of /usr filesystem (among others), as such:
# dump -0uan -f - /usr | gzip -7 > /tmp/20031007-usr-lvl0.dump.gz

This seemed to work as expected, here is some info about the gz file:
% gzip -l 20031007-usr-lvl0.dump.gz
compressed  uncompr. ratio uncompressed_name
507027476 1590855680  68.1% 20031007-usr-lvl0.dump

Everything so far so good.  Today (Oct 22) I tried an incremental dump, 
as such:
# dump -5uan -f - /usr | gzip -7 > /tmp/20031022-usr-lvl5.dump.gz

Here is where I start getting confused.  While my other incremental 
backups today (/ and /var), seemed to be fine, the /usr dump was huge.  
Here is info about the gz file:
% gzip -l 20031022-usr-lvl5.dump.gz
compressed  uncompr. ratio uncompressed_name
527112624 543600640   3.0% 20031022-usr-lvl5.dump

This incremental backup is larger than the original full dump.  Also 
notice that the compression ratio was 3.0%.  When examining the list of 
files dumped, I don't see anything that could lead to a file size like 
this.  A rough count shows that the backup should have been roughly 
11MB uncompressed, compared to the 518MB uncompressed.  I've tried 
reading up on both dump and gzip, but haven't found a clue.  Perhaps 
I've discovered dark matter.

Thanks,
   Ryan