Huge filesystem overhead on USB thumb drive?

[Chanchao]

I have an ext3 filesystem on a partition of a USB thumbdrive. I use this
to keep my files and settings when booting the live cd. (Persistent).

When I boot normally (live cd, not persistent) and right click the
casper-rw partition and go 'properties', I get around 60 MB total.

However when I check in GParted, I note that almost double that is used!
Indeed I run out of space (filesystem full) so I had to increase the
size. 

But... Why is there such a huge overhead?  I did do an 'fsck.ext3' but
it reported no problems.

Anyone know what's going on and how I can get space back? Should I be
using a different file system?

Cheers,
Chanchao