SCSI emulation

Published

There are different SCSI computer storage emulation platforms available to replace real SCSI disks or CDROM drives.

The following 2 emulators are Open-Source hardware.

I choose to evaluate the BlueSCSI emulator, because it is cheaper (~ 60 Euro) and it is available with a Centronics-SCSI connector. It can be purchased from several small companies either as a kit or a fully assembled product. My order of the fully assembled BlueSCSI from One Geek Army was delivered in good condition and worked just out of the box.

I use the BlueSCSI by plugging it into an external SCSI device, which can then be easily connected to my SGI machines. The image below shows the BlueSCSI plugged into a tape drive and connected to my O2.

BlueSCSI on SGI

Note, that the external device does not need to be powered on. BlueSCSI takes power from the SCSI bus.

Up to 7 SCSI devices can be emulated with BlueSCSI by copying files onto the SD-Card, which is inserted into the BlueSCSI.

The files must be named according to the scheme as described in the BlueSCSI manual.

For emulation of CDROM drives, just copy the corresponding ISO file onto the SD-Card and rename it to ex. CD10_MyIrixCD.iso.

For emulation of a hard disk, create a file of the desired disk size containing zeros. I used a command like follows in a Debian virtual machine:

dd if=/dev/zero of="HD20 SGI.hda" bs=1M count=40000

This creates a hard disk file with 40 GB, which will be available on the SCSI bus with ID 2. It must be initialized after connecting the BlueSCSI to the SGI. Just double-click onto the disk icon on the IRIX desktop and choose to initialize the disk from the tasks window. Then add the new disk to /etc/fstab or mount it manually:

mount -t xfs -o rw /dev/dsk/dks1d2s7 /mnt

I made some performance tests to check the speed of the emulation against the internal SCSI disk. As test suite I compiled the Tcl 8.6.17 sources using gcc 3.4.6.

Disk type           Time(min)   Factor
--------------------------------------
Internal disk              34     1.00
BlueSCSI (V30 card)        37     1.09
BlueSCSI (V10 card)        57     1.70

Using BlueSCSI with a V30 SD-card is slightly slower than the internal disk. As the internal drives of my SGI workstations only have capacities from 4 to 7 GB, this slow-down is acceptable due to the major disk capacity increase and increased flexibility.