st driver runs async only

[hgweigand@wiesbaden.netsurf.de (Hans-Guenter Weigand)]

While testing my new DLT tape drive the transfer rate never exceeded 3.3
MB/sec. This looks like asynch SCSI transfer, which is much too slow for
a DLT 4000 with compression enabled while dump(8)ing /usr/src and the
like.

The drive's documentation says, it doesn't request syncronous transfers
by default. Now, is the a way to force st(4) to negotiate syncronous
transfers? Relevant lines of dmesg below.

ncr0 at pci0 dev 12 function 0 "Symbios Logic 53c810" rev 0x02: ncr
53c810 fast10 scsi, irq 11
scsibus1 at ncr0: 8 targets
st0 at scsibus1 targ 1 lun 0: <Quantum, DLT4000, D991> SCSI2
1/sequential removable
st0: st0(ncr0:1:0): 10.0 MB/s (100 ns, offset 8)
density code 0x1a, variable blocks, write-protected

-hgw