Huge size difference between main HD and SD clones
 

I'm surely posting an FAQ but I'm puzzlzed by the following :

I regularly clone my main disk, called "Leopard HD" (running actually Snow Leopard 10.6.7) to two different extenal drives, using smart update, and neglecting "repair permissions on Leopard HD".

"Get Info"gives a size of 69,9 GB for Leopard HD and 41.89 GB for the clones.
I'm surprised at the huge difference. I know that SD does'nt copy a lot of files which are recreated at startup,but what can be these 28 GB which are not copied ? Is that normal ?
I must say that the clones work perfectly with no apparent difference from the main disk. Thus my question is purely out of curiosity.
Thanks for any light on the subject.

Hi, Francois. Please send your log to me with the "Send to shirt pocket" button (use "Error during coy" as the issue type) and I'll analyze what's going on.

(It's likely you have a bad mount point/folder in /Volumes.)

Explanation
 

My machine is a Mac Pro (early2008) with 24 GB RAM. As I have VMWare with several OS'es, and go frequently to sleep when VMware is active, there are 2 files,that Dave helped me to find on SD log :
1) /private/var/vm/sleepimage which reached nearly 25 GB
2) /private/var/vm/swapfile0
Of course these files are ignored by SD when copying the main system disk to a bootable clone.
But that explains why my main disk had more than 69 GB, while the clones made with SD were only 42GB.
I erased on the Terminal the first file (sleepimage) and now my main disk has only 44 GB and runs noticeably faster than before.
All my thanks go to Dave who helped me find this explanation to an occurance which really puzzled me.