The Ever-Adaptable SCSI: Adaptec Raises the Bar for Network Performance with Ultra160
May 2000 |
Adaptec's recent release of its new line of Ultra160 SCSI cards is noteworthy, for a variety of reasons. First, it marks the latest round in the escalating performance of PCs in general. At 160MB/sec--that's 160 megabytes--Ultra160 is the fastest way to connect peripherals to hosts. (200MB/sec Fibre Channel is just arriving as of this writing.) Second, Adaptec has gone aggressive with its pricing--actually introducing the line at a price point lower than its previous Ultra2 cards. Third, several of the cards provide simultaneous support for both LVD Ultra160 drives and Ultra2, and earlier SE SCSI drives. Finally, it definitely answers the critics' claim that Ultra2 SCSI was the swan song of the connector.
Clearly, Adaptec has learned from past SCSI marketing problems, and is making the connector much more appealing to this Internet-crazed, new- millennium crowd.
In the Beginning
SCSI's beginnings were pretty humble for those who remember. It is hard to imagine that SCSI has come all the way from 1981, when, at the dawn of PC prehistory, the Shugart Associates Systems Interface (SASI) debuted with--what was it--750KB/sec throughput? In June 1986, this interface became Small Computer Systems Interface (SCSI)--SCSI-1, if you are keeping count). SCSI-1 gave us a screaming 5MB/sec throughput.
At 160MB/sec--that's 160 megabytes--Adaptec's Ultra160 SCSI adapter is the fastest way to connect peripherals to hosts.
We flip ahead to 2000, and we now have a bus capable of 32 times that original throughput--not bad for a 14-year-old technology. More importantly, the bus has become far more intelligent in this iteration.
This couldn't come at a better time for SCSI. With Western Digital quitting the SCSI drive business, there are fewer vendors still producing SCSI hard drives--Quantum, IBM, and Seagate being the only ones touting Ultra160 drives. For those with an optical bent, there are also only a few vendors with DVD or CD readers/writers using the SCSI adapter. They include NEC, AOpen, Plextor, and Pioneer.
And even Plextor, long the home of SCSI-only aficianados, has now turned to offering an ATAPI device.
Adaptec is quick to point out that it isn't a failure of the SCSI technology that made it less popular; it was more a set of business decisions in releasing the previous upgrade. During the introduction of Ultra2 SCSI, the industry did not respond in a coordinated effort. Rather than deliver all the components needed for implementing a full Ultra2 SCSI solution, pieces were released over time.
As a result, for example, there was a lack of both terminators and drives, even though host adapters were readily available. Further, backward-compatibility was downplayed or poorly explained, leaving many users believing they could attach older Ultra SCSI drives to the longer Ultra2 SCSI cables and have them work (which they wouldn't).
This faulty introduction soured many people to SCSI, diverting their attention to the lower-performing but better-understood ATAPI bus. At least there, the system had backward-compatibility and preserved the current hardware investment.
It is clear that this time around, Adaptec would have none of that with the introduction of Ultra160, which not only comes complete and ready to go, but has legacy drive support on most of the cards.
What Puts the Ultra in Ultra160?
The Ultra160 SCSI specification outlines five core and optional features that differentiate it from past SCSI versions. These include:
- Cyclical redundancy checking (CRC), which protects your data from being lost in the event of a poor connection or during a hot-swap of a new drive into the system
- Domain validation, which overcomes a problem with mixing legacy SCSI drives with Ultra160 drives on the same bus. Domain validation checks to see if the bus and drive handle Ultra160 and if so, proceeds at that data transfer rate. If this rate isn't possible, domain validation allows the device to slip to a lower data transfer speed before data transfer begins
- Double-edge clocking, which allows for doubling performance in future versions of the bus, such as Ultra320 and Ultra640
- Packetization, which enables the adapter to send multiple commands, messages, status reports, and other data between SCSI devices in two data phases and at the fastest negotiated data rate. (This is an optional feature of Ultra160 SCSI devices)
- Quick arbitrate and select (QAS), which provides faster arbitration to reduce connect/disconnect time on the SCSI bus. This means that a QAS-supported device can give the bus to a second QAS-supported device that is waiting for bus time. It does this without the delay of having to enter a new arbitration phase. (This is another optional feature for Ultra160)
The challenge here is to differentiate between the Ultra3 specification of the SCSI Trade Association and Adaptec's (and others') version of Ultra3, that is the Ultra160 product line.
Adaptec is reducing the number of its SCSI host adapters down to four with the release of the Ultra160 products. These include two 32-bit PCI cards, the 19160 and 29160N; and two 64-bit cards, the 29160 and 39160.
Adaptec is shipping Ultra160 drivers for all the major platforms including Unix, Linux, Macintosh, NetWare, and Windows. However, it is unclear how complete the coverage will be for all the cards. For example, the 19160 as of January 2000 lacks any Unix or Windows 2000 drivers.
Also, there appear to be only minor differences between the connector configuration of the 19160 and the 29160N. The principal difference between the cards is the LVD cable supplied in the kit.
The 29160N and the 29160 differ in this regard:
The Ultimate Throughput Option
Clearly, having 160MB/sec throughput would seem to be ideal for network performance, and indeed it is. Multiple users' addressing multiple drives on the server demands this kind of horsepower. For optical drive users, this newer bus speed allows administrators to position more drives on a single bus while still delivering full drive speeds. Users looking at contemporary RAID solutions will also find the Ultra160 specification a no-brainer for upgrades or new systems.
All administrators will have SCSI playing a role in their systems for at least the next five years and beyond.
However, this doesn't mean that you'll necessarily see 160MB/sec throughput on a given network server. This higher level of performance reveals several new bottlenecks. First, RAM bus throughput only reached 125MB/sec with SD RAM, the type of RAM most commonly in use today. Second, the PCI 2.1 bus burst speed is only 133 MB/sec, of which only 110MB/sec is actually usable once you subtract I/O overhead. So even if the RAID or SCSI controller can retrieve or write data at 160MB/sec, the bus the card plugs into may be a bottleneck.
For those power-hungry users looking for the ultimate I/O solution on a standalone high-end system, the question is a little less clear. Standalones run into those same problems as network servers with RAM and PCI bus speeds. Finally, most hard drives don't sustain even a quarter of this throughput. Contemporary SCSI drives sustain 30-40 MB/sec at most. Network servers don't have a problem here, since they often have four or more drives either in a RAID configuration or as separate volumes. Together they demand the full 160MB/sec throughput, but a single drive wouldn't see any benefit in using Ultra160 over Ultra SCSI.
But in the server RAID environment, the Ultra160 truly shines. Adaptec knows this, and offers three RAID host adapters that are extensions of their SCSI cards: the AdvancedRAID 2310 ($669), 2620 ($1075), and 3640 ($1995). The 3640 can support upwards of 2TB of RAID storage with 60 drives.
No discussion about SCSI today can ignore SANs and Fibre Channel. Many take it for granted that all storage will move to the SAN model in the near future. But ask system administrators about SANs, and you may find a few surprises. Peripheral Concepts, a research company based in Santa Barbara, California, asked 50 IT managers in 1999 if they knew about SANs. Fifty percent of them did not. At the annual Fibre Channel Conference in San Francisco last fall, out of 1,000 attendees, only a handful were actual end-users. The rest were vendor personnel.
Of course, all the predictors suggest that Fibre Channel is to be a booming market. Peripheral Concepts says $10 billion in 2000, $20 billion by 2002. Framingham, Massachusetts-based International Data Corporation (IDC) is a little more conservative, predicting $7.5B in 2000, $15B in 2002.
On the other hand, IDC also says that the number of drives shipped with Fibre Channel connections won't surpass SCSI/ATAPI anytime before 2002, and probably for quite a while after that.
It certainly isn't a question of which connection is to be the dominant one. Arguing Fibre Channel versus SCSI is a dead issue because they are both needed. What the numbers show is interesting. Even given the rapidly expanding sales of Fibre Channel, SCSI remains a major player. So all administrators will have SCSI playing a role in their systems for at least the next five years and beyond.
None of the predictions show a rapidly diminishing and/or vanishing SCSI technology. In fact, the introduction of Ultra160 (and the tantalizing prospect of Ultra 320, Ultra 640, and the like) gives this technology every bit of the cachet that Fibre Channel might hope to claim.
The plummeting cost of hard disk space (notice the under-$200 price point for 30GB drives?) now makes RAID the standard, not a higher-cost option, for network storage. Both desktops and servers can now employ this protection, which should mean a longer life for SCSI.
SCSI in the New Millennium
Adaptec may have hit a home run with Ultra160. But the series isn't over yet. Just because Adaptec can create the SCSI standard adapter doesn't mean it can't go the way of Hayes. (Remember them? We all use a Hayes-compatible modem, even though there's no more Hayes.)
In looking over the Ultra160 cards, we can't really fault Adaptec on approach or delivery. The only arguments that remain are in the field of battle: is this the tool for the future, or is the path to SCSI now making its way to commodity SCSI, ATAPI, and others?
Which is it? Ultra160 or Ultra3?
Our penchant for inventing terms hasn't stopped with the arrival of Ultra160. Now we can also talk about Ultra3 SCSI, which is either a superset of Ultra160 or a subset, depending on whom you ask. According to the SCSI Trade Association (STA), the moniker Ultra3 describes the following: "A 16-bit 160MB/sec SCSI connection of up to 12 meters (40 feet) between a host and up to 16 Low Voltage Differential (LVD) devices."
Ultra160, on the other hand, is a commercial term created by vendors to promote a specific implementation of Ultra3 that also includes Fast-80DT, CRC, and Domain Validation--which are not, strictly speaking, requirements of Ultra3. However, the STA says "most" Ultra3 devices will use these features. The primary difference will be with packetization and Quick Arbitrate and Select (QAS), which are definite options for Ultra3 SCSI.
If we look at Adaptec's description of Ultra160, we have "a 16-bit 160MB/sec SCSI adapter supporting a 64-bit PCI interface, with up to 30 LVD devices (15 per channel)" using the company's 39160 card. To Adaptec, Ultra160 is a superset of Ultra2 SCSI.
This means that the Ultra3 spec includes Ultra160, but not all Ultra160 cards and devices work well with Ultra3 cards and devices or vice-versa. So any two Ultra3 SCSI devices may not communicate at 160MB/sec if they don't include the same set of features. Finally, Ultra160 SCSI host adapters do support Ultra2 SCSI devices in Ultra2 SCSI modes. Even Adaptec saw some humor in this, as it noted that the flexible Ultra3 spec might even include UltraDMA (since it too uses Double Transition Clocking), or worse yet, Ethernet itself.
So you'd now expect that the STA names for the follow-ons to Ultra3 would be Ultra4 and Ultra 5, right? Well
don't get confused because the STA has selected the names Ultra320 and Ultra640 as the follow-ons to Ultra3, and not Ultra4 or Ultra5. (Maybe the Ultra160 vendors had a good idea after all?) The Ultra320 and Ultra640 lines will use all five of the features discussed.
Companies Mentioned in This Article
691 South Milpitas Boulevard, Milpitas, CA 95035; 408/945-8600, 800/442-7274; Fax 408/262-2533; http://www.adaptec.com
The SCSI Trade Association
404 Balboa Street, San Francisco, CA 94118; 415/750-8351; http://www.scsita.org
Ultra160 Web site
NETWORKOBSERVER columnist David Doering (email@example.com), an EMedia contributing editor, is also senior analyst with TechVoice Inc., an Orem, Utah-based consultancy.
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