Well, I did some additional testing and found the problem was in the B2D configuration. I also backtracked what I did.
My B2D were always configured with 1GByte files, the default BE setting, and never had any problems withmakeing backups. Since a few weeks/months backups were still running in the morning when I arrivied at work. (verify/duplicate). The only thing changed was, I applied SP3 and condensed my backup jobs from about eleven to two. (because of timewindow problems)
When I was monitoring network traffic, I thought the problem was somewere there to be found, I noticed that the data transfer paused for about 2 minutes and resumed afterwards. The same time BE was 'loading media' of the backup in question. Strange thing was that this happend every about every 1GByte, the same size as my B2D files.
To test this I reconfigured the B2D devices in question and gave them roughly half the size of the amount of data being backed upped.
It seems BE needs about 2 minutes to mount a B2D device before it can use it for backup purposes. Given the fact that my backup jobs were 72.5 GB and 13GB, and B2D configured for 1GB files, this would mean about 85x2 minutes were wasted on waiting for BE to become ready. (don't ask me why it takes 2 minutes to mount a file)
I reconfigured one B2D device to use a 50GB file and the other one a 60GB file. This morning all my backups were finished before I came in the office.
Job1
Before : 72.5 GB to B2D in 14:28, duplicate to tape in 3:35
Now : 72.5 GB to B2D in 8:27, duplicate to tape in 1:26
Job2
Before : 13.1GB to B2D in 6:13, duplicate to tape in 2:07
Now : 14.1 GB to B2D in 5:04, duplicate to tape in 00:33
Quit a time saver. I still have to reconfigure my weekend backup which is around 306GB. With B2D files of 100GB each I expect it will be finished quit some time earlier than before.
So the configured size of your B2D device IS important with respect to the performance of BE. (don't know how this is in SP4, I would like to know that. Maby some can test this ?)
Regards
A van der Boom