Using Smart Update in a smart way?

[efefes]

Hi, I have a question on how to use Superduper’s Smart Update.

I have a Lacie disk on which I use Timemachine and recently changed another Lacie drive for a Drobo. The Drobo is connected through USB on my Airport Extreme and I connect wireless to it. The Drobo is used for several archives but also for Superduper using .sparse images.

I have installed all the latest updates and firmware and run Snow Leopard myself.

Superduper is set-up to use smart copy, all files. The only exclusion (ignore in the script) is my Parallel Windows XP virtual machine as that is only used for Exchange Mail.

I want to use Superduper daily but it takes very long to finish. As I thought it looked like the number of changed files was very high I did a small experiment today.

1)
I quit all my programs and also disabled timemachine. I then started Superduper to smart copy using yesterday’s .Sparse image. This smartcopy ran for over two hours and these were the stats: 619.500 files evaluated, 173.055 files copied, copy speed 13,45 MB/s 118 GB evaluated, 9,1 GB copied.

During the backup I did not touch my Macbook.

2)
Immediately after Superduper completed I used Superduper again with exactly the same set-up. Again, after the first Superduper job ended and this one started I didn't use my Macbook and only 5 minutes were between the end of job 1) and the start of this second job.

This time it ran for over an hour and these were the stats:
619.503 files evaluated, 172.648 files copied, copy speed 22,15 MB/sec, 118 GB evaluated and over 2,43 GB copied.

My question is therefore: is this normal behavior: in other words where does this 2,4 GB of changes come from and how should I configure Superduper to avoid this?