removing and adding scsi-devices
To remove a scsi device with current (2.6.16) linux kernels use
echo 1 > /sys/class/scsi_host/hostH/device/targetH:B:T/H:B:T:L/delete
and to add them initiate a scan with
echo B T L > /sys/class/scsi_host/hostH/scan
Thanks to maks for the tips.