With the SCSG device type you can map SCSI devices to the generic SCSI driver of Linux (SG 3). Therefore SCSG can represent any device supported by this driver. These cover in particular mass storage devices.
Therefore SCSI2Pi since version 5.0 can also be used as a USB-to-SCSI bridge. Binaries of the development version are already available.
The SCSG type requires a device file /dev/sg* as a parameter. Linux automatically creates these device files when a device supported by the Linux SG driver is connected, e.g. a USB stick, a USB hard drive or a USB DVD drive. Even USB floppy disk drives have successfully been tested.
lsscsi --generic lists all devices managed by the Linux SG driver and the respective device files:
>lsscsi --generic [0:0:0:0] disk Y-E DATA USB-FDU 4.01 /dev/sdc /dev/sg3 [1:0:0:0] disk Generic MassStorageClass 2011 /dev/sda /dev/sg0 [1:0:0:1] disk Generic MassStorageClass 2011 /dev/sdb /dev/sg1 [2:0:0:0] cd/dvd TSSTcorp CDDVDW SN-208AB LA02 /dev/sr0 /dev/sg2
With this information you can create bridges for the USB floppy disk drive and the DVD drive, for instance:
>s2p -i 4 /dev/sg3 -i 5 /dev/sg2
There are no image files with the SCSG device type. s2p forwards all SCSI commands directly to a connected device. SCSG therefore does not emulate a particular device, but represents a real device connected to the Pi.