I seem to have a weird backup situation here

I am running backups in a test environment. I'm testing large arrays for file
servers.
The 1st sel backup took around 9hrs (80GB), subsequent sel backups are taking
around 19hrs to complete.

As I am only running sel backups I figure the ADSM database should not be
processed for the next backup to run. Even if it was it shouldn't take 19hrs.
The weird thing is that if I change the drive letter so that ADSM thinks the
data is from a new file system the backup time is back to around 9hrs.

This is quite puzzling.
Can anyone out there shed some light on this.



TIA


Toni