The SCSI To Ethernet Connection

THE SCSI - TO - ETHERNET CONNECTION

Image by Andrew Faulkner

Short on slots? Take the SCSI route to faster networks
By Joel Snyder

MacWorld, Jan 1994 pages 171-173 on Internet Archive

Need to upgrade your LocalTalk network to Ethernet speeds, but can’t spare internal slots for network interface cards? Use the SCSI bus.

While many Macintoshes don’t have enough internal slots to go around, nearly all Macs (except the venerable 128K, 512K and the new PowerBook Duos) have external SCSI connectors.

Eight companies sell 17 different SCSI-to-Ethernet adapters at prices ranging from about $200 to $700. With the SCSI port on one side of these boxes connected to a Mac, and the Ethernet port on the other side connected to a network cable, Macs that already have a full complement of internal cards (or even those built without internal slots) can be networked at speeds several times faster than LocalTalk’s.

Despite the $500 price range, all 17 adapters do basically the same thing at similar performance levels. Some SCSI-to-Ethernet adapters perform better than others, but the variations are so minute that you probably won’t notice them. Instead, look for features that suit your particular needs, such as types of Ethernet connectors supported, configuration flexibility, form factor, and compatibility.

SCSI-to-Ethernet Adapters Compared

Connector Support

Ethernet networks generally use a combination of different wires (media). Each wire type — including 10BaseT (twisted pair), 10Base2 (colloquially dubbed thin net), and 10Base5 (thick net) — has its own type of connector. To accommodate the variety of network media, adapters come in several different configurations, offering connectors for one, two, or all three types of wire. (“SCSI-to-Ethemet Adapters Compared” shows which connectors each adapter supports.)

Dayna is the most flexible in this area, with its DaynaPort SCSI/ Link-3. The SCSI/Link-3 is the only SCSI-to-Ethemet adapter that offers connectors to all three types of wire, in one small box.

The Cabletron EA414 is the only adapter compatible with fiber-optic cabling and the FOIRL (Fiber Optic Inter-Repeater Link) standard.

Configuration Flexibility

Most SCSI-to-Ethernet adapters automatically sense which Ethernet media has been connected and set themselves accordingly. All the autosensing adapters I looked at worked fine except the Cabletron EA412, which required manual intervention some of the time.

Two companies make adapters that don’t sense which kind of network is attached, but the Compatible Systems design (also sold by Technology Works and Focus Enhancements) requires the most fussing. Changing its media type requires removing two screws, changing a jumper, and replacing the screws. The MaCNet adapter has a switch on the back that simplifies the process somewhat.

Connecting devices to a SCSI chain requires some flexibility. One device usually isn’t a problem, but when you have a string of them you must get the SCSI IDs, termination, and all the possible connectors right.

All of the adapters tested have a switch to select SCSI IDs. When adding an adapter to an existing Macintosh, remember that SCSI ID 7 is reserved for the Macintosh CPU, while SCSI ID 0 is usually assigned to the internal hard disk.

Dayna, Farallon, and MaCNet adapters have the greatest SCSI connection flexibility. Their adapters allow either a terminated or an unterminated SCSI chain, and each adapter has two SCSI connectors. That makes it simple to plug one of these two connectors into an existing chain of SCSI devices. Other companies’ adapters require special Y-cables (included with Asante adapters, optional with all the other adapters) or don’t allow for the adapter to be anywhere but at the end of a SCSI chain.

Portability

For administrators who tote PowerBooks around the network, or for other users on the go, the size and weight of the adapter is crucial. Asante’s adapters, each the size of a small paperback book, weigh in at a light 6 ounces. Cabletron’s are only a few inches longer and a couple of ounces heavier, but cost anywhere from $150 to $350 more.

For the PowerBook user, the external transformer can be heavy, and an AC outlet has to be available at all times. Since all but one of the SCSI-to-Ethernet adapters use the same power connector and a 12 -volt power supply, you can get around the outlet restriction by powering your adapter with a 12V battery pack (eight AA-batteries). Unfortunately, such a pack weighs about the same as a transformer, if not a little more.

Watch out for another PowerBook quirk: PowerBooks require an unusual SCSI cable. Some companies sell PowerBook versions of their adapters, which simply include the special cable, at a higher price than adapters that include a standard Mac SCSI cable. Others sell the cable as an add-on, for as much as $50 extra. Asante solves the problem by including both PowerBook and standard Mac cables with all of its adapters.

Compatibility

In most cases all of the adapters performed flawlessly on all platforms tested. But two did experience problems: The DaynaPort SCSI/Link-3 usually worked fine, but did randomly fail some tests, crashing the Macintoshes and twice bringing down the entire AppleTalk network. Eventually the adapter worked, but Dayna wasn’t able to isolate the cause of the crashes. The Cabletron EA412 worked well on the Macintosh II but was unable to receive large files over TCP/IP when connected to a PowerBook.

Performance Issues

In general use, all the adapters I tested turned in equivalent performances.

Transferring data to a Macintosh disk from the network performed quite poorly, between .18 and .28 Mbps. Transfers from Macintosh disks out to the network were much faster, ranging from .17 to .48 Mbps.

For TCP/IP and AppleShare network applications, it doesn’t matter what adapter you buy: they all run at about the same speed. For special-purpose applications, such as Ethernet protocol-analysis, the Asante Mini-series adapters turned in the fastest performance, while the Compatible Systems (and Technology Works and Focus Enhancements) adapters did the worst.

Decisions, Decisions

If your budget isn’t tight, consider buying Asante’s Mini EN/SC. The smallest and lightest of the bunch, it is priced toward the middle of the pack. Plus, it comes with a high-speed driver, which gives it a significant performance edge in a few applications.

For applications where different media could show up at any moment, the DaynaPort SCSI/Link-3 ($499 for PowerBooks) is an obvious choice because it offers every possible connector in one box. Be careful, though: Dayna may not have worked all the bugs out of this one. Test in your own environment before buying.

If you want to use the most common networks, AppleTalk or TCP/IP, from a desktop Mac and you aren’t picky about the refinements, the Focus Enhancements EtherLAN SC adapter is the best choice. The EtherLAN SC (based on the Compatible Systems Ether+ design) is more difficult to configure, heavier, and slower than many of the other adapters; but for basic functionality, the $225 price is hard to beat. So, pick an adapter and put even your slotless Macs on Ethernet through SCSI today.

JOEL SNYDER is senior analyst with Opus One, a consulting firm located in Tucson, Arizona. He specializes in networks and international aspects of information technology