SCSI too slow

[Karsten Fuhrmann]

Hello,
i am using a Adaptec 29160UW Controller in my FreeBSD 4.8 Box together 
with an Easyraid 2 external RAID System and a Quantum SDLT-320 Drive.
The problem is the data transfer Rate of my SCSI Channel is only 40 
Mbytes/s.

dmesg shows
da0: <easyRAID II > Fixed Direct Access SCSI-2 device
Jun  8 16:17:17 stern /kernel: da0: 40.000MB/s transfers (20.000MHz, 
offset 31, 16bit), Tagged Queueing Enabled

Is there a way to change the transfer rate somehow, because at least my 
SDLT is an ultra wide SCSI (LVD/SE)

Cheers,
karsten