FAQ: Considerations for Ratoc's FireWire and USB 2.0 to SCSI Adapters

SCSI long ruled the performance peripheral category for storage and other devices. With many advantages over competing busses, including flexibility, speed, and reliability, SCSI devices are found everywhere. However, as computing platforms move towards cheaper internal busses and serial busses in general, finding SCSI host adapters capable of interfacing with older SCSI devices has become difficult. SCSI itself is transitioning to SAS (Serial Attached SCSI). On the newer desktop realm, the few PCIe SCSI host adapters are expensive. For newer laptops, there aren't any ExpressCard to SCSI host adapters we are aware of. This brings us to SCSI host adapters utilizing external busses like high performance FireWire and prosaic USB. While Ratoc's FireWire and USB to SCSI adapters have been on the market for quite some time, they are beginning to grow in popularity since they are an inexpensive and accessible way to work with older SCSI devices. This document is intended to clear up some of the confusion over deploying Ratoc adapters with SCSI devices.

FireWire To Ultra SCSI: FW-USCSI-01; Ratoc FireWire to Ultra SCSI Converter; FireWire to Ultra SCSI adapters have the advantage of a much faster host connection than USB, and FireWire is superior to USB in every regard.

USB To Ultra SCSI: USB-USCSI-01; Ratoc USB 2.0 to Ultra SCSI Converter; USB 2.0 to Ultra SCSI adapters can be used with a number of SCSI devices.

USB To Ultra Wide SCSI: USB-UWSCSI-01; Ratoc USB 2.0 to Ultra Wide SCSI Converter U2SCX-LVD; USB 2.0 to Ultra SCSI adapters can be used with Ultra Wide SCSI Devices.

Ratoc offers three SCSI host adapter models: The FR1SX (FW-USCSI-01) FireWire to Ultra SCSI, the U2SCX (USB-USCSI-01) USB to Ultra SCSI, and the U2SCX-LVD (USB-UWSCSI-01) USB to Ultra Wide SCSI. The FR1SX and U2SCX feature a HD-50 connector and are native Ultra SCSI devices. They are backwards and forward compatible with many other SCSI standards when used with connector adapters. While both rated to handle Ultra SCSI throughput of 20MB/s, the FR1SX tends to realize much better sustained throughput since FireWire isn't hampered by USB 2.0's CPU utilization overhead. The U2SCX-LVD features a HD-68 connector and is a native Ultra Wide SCSI device. It is also backward and forward compatible with many other SCSI standards when used with connector adapters. U2SCX-LVD is rated as handling Ultra Wide SCSI throughput of 40MB/s, however this maximum is doubtful since nearly any real world benchmark of USB 2.0 sustained throughput maxes out at around 33MB/s. That said, it is faster than the U2SCX, albeit considerably more expensive. When the better performance of the U2SCX-LVD isn't paramount, many customers prefer the U2SCX with a High Density 50F to High Density 68M Adapter combination over the U2SCX-LVD since is over $150 cheaper.

Termination Power or Term Power

All Ratoc SCSI host adapters require power to operate. That power is supplied either by an optional (purchased separately) AC adapter, or through drawing power off the SCSI buses' Term Power. In order to use Term Power, the SCSI device the Ratoc adapter is connected to must provide it. This invariably brings up two questions: what is Term Power, and does my device provide it? Answering the first question, according to the SCSI Trade Association:

"Terminators are powered from the "term power" line on the SCSI bus. Term power can come from any device on the bus, and is provided by either the host, a drive on the bus, the backplane, or any combination thereof. Term power is provided through a diode and fuse - historically - the drop across the diode and cable allows for a term power range of 4.0 to 5.25 volts."

As for the second question one must consult with the SCSI device's manufacturer or documentation. If the SCSI device doesn't provide Termination Power, then purchase the optional PS-5V2A 5VDC 2A External Power Supply/Adapter ST (USB/SCSI) power supply, or find an AC adapter with the same specifications at a local supplier.

Bear in mind termination (ie. terminating resistors) and termination power are not the same thing. The presence of an external terminating resistor, or a switch for an internal terminating resistor, have no bearing or whether a SCSI device provides termination power.

SCSI Connectors

There has been a whole range of SCSI connectors over the years. Part of the confusion people run into is that there is overlap between SCSI standards and connectors. In other words, several connectors are applicable to single SCSI standards. As this document focuses on device compatibility with Ratoc SCSI adapters, it will not address internal SCSI connectors. While roughly ten different external SCSI connectors exist, there are four in particular that are the most commonly found. The following drawings depict the four more common SCSI connectors with the types featured on Ratoc's host adapters indicated in parenthesis.

If your SCSI device's connection doesn't match the connector present on a Ratoc host adapter, then a low cost adapter plug employed between the connectors will allow its use. Synchrotech carries three types of adapters that take the FR1SX and U2SCX HD-50 connector and provide an alternate connector on the other side. Synchrotech doesn't stock any converters for the U2SCX-LVD since it is typically used with 68-pin LVD type devices to begin with.

Using the Ratoc FR1SX or U2SCX with a SCSI device featuring a HD50F

Ratoc's FR1SX or U2SCX plug directly into SCSI devices featuring female HD50 (50 pin) connectors.

Using the Ratoc FR1SX or U2SCX with a SCSI device featuring a C50F

To use Ratoc's FR1SX or U2SCX with a SCSI device featuring a female C50 (50 pin Centronics style) connector, use the SCSI-RCL3005 High Density 50F to Centronics 50M adapter (Ultra to Fast SCSI I/II).
The bottom four images are the SCSI-RCL3005 pin-outs as a line drawing on the left and a photograph on the right. One side of the connector receives the FR1SX or U2SCX (images in top row) and the other side plugs into the SCSI peripheral (images in bottom row).

Using the Ratoc FR1SX or U2SCX with a SCSI device featuring a HD68F

To use Ratoc's FR1SX or U2SCX with a SCSI device featuring a female HD68 (68 pin) connector, use the SCSI-RCL3068 High Density 50F to High Density 68M Adapter (Ultra to Ultra Wide/LVD SCSI).
The bottom four images are the SCSI-RCL3068 pin-outs as a line drawing on the left and a photograph on the right. One side of the connector receives the FR1SX or U2SCX (images in top row) and the other side plugs into the SCSI peripheral (images in bottom row).

Using the Ratoc FR1SX or U2SCX with a SCSI device featuring a DB25F

To use Ratoc's FR1SX or U2SCX with a SCSI device featuring a female DB25 (25 pin 'Mac' style) connector, use the SCSI-RCL3025 High Density 50F to D-Sub 25M Adapter (Ultra to Fast SCSI I/II Mac).
The bottom four images are the SCSI-RCL3025 pin-outs as a line drawing on the left and a photograph on the right. One side of the connector receives the FR1SX or U2SCX (images in top row) and the other side plugs into the SCSI peripheral (images in bottom row).

Using the Ratoc host adapters with other types of SCSI connectors

There are other types of SCSI connectors, converter plugs, and gender changers on the market. Some companies to investigate for alternate connectors and converters are Granite Digital, The Mate Company, and Paralan Corporation. There are several to choose from and the preceding list is provided as a service, not an endorsement or recommendation.

Important FR1SX FireWire to Ultra SCSI Information

Before purchasing the FR1SX FireWire to Ultra SCSI host adapter, check Ratoc's system requirements and compatibility lists carefully.

Important U2SCX USB 2.0 to Ultra SCSI Information

Before purchasing the U2SCX USB 2.0 to Ultra SCSI host adapter, check Ratoc's system requirements and compatibility lists carefully.

Important U2SCX-LVD USB 2.0 to Ultra Wide SCSI Information

Before purchasing the U2SCX-LVD USB 2.0 to Ultra Wide SCSI host adapter, check Ratoc's system requirements and compatibility lists carefully.

More Useful SCSI Information

Overview of SCSI Standards and Cables: http://www.scsita.org/terms/SCSI_Overview.html
Visual Guide to SCSI Connectors: http://www.scsita.org/aboutscsi/Pictures.html
The 7 Generations of SCSI: http://www.scsita.org/aboutscsi/7gen.html
Overview of SCSI Standards and Cables: http://www.scsita.org/aboutscsi/SCSI_Overview.html
SCSI Termination Tutorial: http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html
STA-Endorsed Terms and Terminology for SCSI: http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html#Table1

Ratoc FireWire and USB solutions for Internal SCSI Devices

The connectors on internal SCSI devices differ from those found on external devices. Further, pre SCA style devices also require power connectors (typically Molex style). None of the Ratoc FireWire or USB (FR1SX, U2SCX, or U2SCX-LVD) work with IDC Header or SCA internal SCSI devices.

A solution to this is to purchase and external enclosure for the internal SCSI device and then connect it to the host system using one of the Ratoc solution. External SCSI enclosures can be special ordered from specialty stores.

Ultra Wide SCSI, Ratoc, FireWire, USB

FAQ: Considerations for Ratoc's FireWire and USB 2.0 to SCSI Adapters