ATA Goes Beyond the Desktop

Hard Drive Update

By Heidi Biggar

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Once viewed as strictly a desktop or mobile play, parallel IDE-specifically, Ultra ATA/100-has been making great strides in traditional high-end SCSI markets. Problems with its performance, capacity, and even scalability have become relative non-issues, and a roadmap has been defined for a faster, serial interface.

In certain markets and for certain applications, ATA can be a low-cost alternative to SCSI. As a result, analysts expect ATA to penetrate entry-level server, RAID, and network-attached storage (NAS) segments. "There's no doubt that ATA is going to invade this market," says Dave Reinsel, senior research analyst at International Data Corp. "It's already happening."

The net result is a blurring of desktop and high-end markets. Performance, capacity, throughput, and host-utilization of the two interfaces are roughly the same, but pricing can vary by as much as two to three times. However, Seagate this month is expected to unveil a high-end SCSI drive that will be priced similarly to ATA.

This price differential has caught the attention of users and vendors alike, leaving drive manufacturers, including Fujitsu, IBM, Maxtor, Quantum, and Seagate, scrambling to compete for a share of the expanding entry-level server market.

"It's a small market, but it's got significant growth potential," says Pat McGarrah, director of strategic and technical marketing at Quantum. According to IDC, entry-level server shipments are expected to post an overall 24% CAGR for the period 1999 to 2004, compared to -4% and 4%, respectively, for workstation and multi-user segments. Desktop-class hard drives are expected to account for some 20% of these shipments by 2004.

This integration will result in some cannabalism of the SCSI opportunity and the expansion of the drive market by offering users, who otherwise couldn't afford SCSI or Fibre Channel technology, a low-cost RAID solution, says Dave Reinsel in the IDC report Worldwide Hard Disk Drive Market Forecast and Analysis, 1998-2004.

"This segment is extremely competitive," says Greg Piligian, director of Ultrastar business line management at IBM. Seagate, for example, this month will begin volume shipments of Barracuda III, a 7,200rpm Ultra ATA/100 drive with capacities to 40GB. And Fujitsu says it will soon deliver a 20GB-per-platter ATA drive in 5,400rpm and 7,200rpm speeds.

Meanwhile, Maxtor continues to ramp production of its August-announced DiamondMax series. With up to 80GB of capacity, the 5,400rpm DiamondMax 80 is currently the highest-capacity SCSI or ATA drive on the market, though still-higher-capacity drives are expected to be announced in the Comdex time frame. In addition to the DiamondMax 80, Maxtor began shipping a 45GB 7,200rpm drive (DiamondMax Plus 45) and a 40GB 5,400rpm model (DiamondMax VL 40). All three drives support the Ultra ATA/100 interface.

IBM and Quantum, developer of the ATA interface, announced 7,200rpm Ultra ATA/100 drives earlier this summer. Western Digital is also manufacturing ATA drives, but declined to comment on any plans to expand beyond the desktop. Western Digital exited the high-end drive market last year. Hitachi, also an ATA drive manufacturer, focuses solely on mobile applications.

ATA drives currently account for about 2% of all high-end drive shipments and about 98% of all desktop units (see diagram in Fibre Channel sidebar on p. 24). For the past two quarters, Seagate has been the top supplier of ATA drives, followed by Quantum, Maxtor, and Western Digital.

ATA trends

The so-called "sweet spot" of the entry-level server market is currently 7,200/ 10,000rpm SCSI, but that's expected to change as higher-performance, higher-capacity ATA drives become more mainstream and the industry transitions to 10,000rpm technology.

"There is an interesting dynamic going on here," says IDC's Reinsel. "7,200 SCSI is on the decline and is basically going to be replaced by 7,200 ATA." Many of these devices are expected to find homes in ATA-RAID boxes or small servers where performance deficits are masked by controllers.

"Eighty-percent of our drives end up behind a RAID controller," says Quantum's McGarrah. "Once you do that, you lose all the benefits of whatever interface you're talking to. It's the controller that brings the value." ATA-RAID controller vendors include Arco Computer Products, 3Ware, CMD, and Promise Technology.

Consider the following two examples: A RAID box with SCSI connectivity on the front-end and ATA drives on the back-end and a low-end NAS device (e.g., Quantum Snap! or Maxtor MaxAttach) equipped with Ethernet 10/100 into the box and ATA behind the controller.

In either case, the "ATA-ness" of the hard drive is hidden from the front-end by the controller, blurring the features of SCSI, ATA, and even Fibre Channel. "You notice performance, you notice some of the caching, but you don't necessarily notice the interface itself," says McGarrah.

However, in JBOD (Just a Bunch of Disks) configurations or in multi-user applications, ATA does not excel. In these arrangements, users benefit from the rich feature sets of traditional high-end interfaces, such as SCSI or Fibre Channel, which bring additional functionality to the table.

"SCSI will continue to dominate in multi-user, multi-threaded applications," says Jack Schiffhauer, performance storage business line manager, IBM. "SCSI supports more drives per bus, thus enabling more capacity and data throughput than ATA."

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Last month, however, start-up Alcita Technologies, a Woburn, MA-based provider of integration and optimization products, announced IDEplex2 an ATA-to-SCSI converter that could have significant implications for ATA technology (see sidebar "SCSI functionality at ATA pricing" on p. 26).

Also on the horizon are 10,000rpm ATA drives and, perhaps most notably, a higher-performance serial interface (see sidebar on p. 24).

A comparison

ATA has caught up to SCSI in terms of performance, and in the case of capacity has a slight advantage-at least for now. The Ultra ATA/100 interface, which was announced by Quantum in June, has a 100MBps transfer rate, up from 66MBps, and a 150MBps serial interface is being developed. On the SCSI front, although Ultra160 continues to ramp up, 80MBps Ultra SCSI is still the favored interface among entry-level servers, according to the IDC report.

Despite ATA's advantages, the interface has some significant shortcomings, including lower access times, limited scalability, no hot-plug capability, the inability to service multiple I/O requests, and short cable lengths.

  • Performance: For equivalent rpm drives, data rates are similar for both technologies-neither exceeds the bus rate-and latency is the same. SCSI drives have the edge in terms of seek times; a typical SCSI drive features a 6ms seek time, 8ms+ for ATA. SCSI drives may also have larger caches.
  • Scalability: The ATA interface allows for a maximum 19-inch cable length and a two-drive-per-bus ratio, compared to 6m and 15:1 ratio for SCSI. This severely limits the scalability of the ATA interface. Also, SCSI's bus architecture, as opposed to ATA's point-to-point structure, enables users to hot-plug drives. This is not possible with ATA technology.

For improved scalability, users can integrate multiple ATA buses behind a RAID controller or use a converter, such as Alcita's IDEplex2, to bridge from ATA to SCSI at the drive level.

  • I/O processing: Unlike SCSI, ATA cannot service multiple transactions, or multiple reconnect/disconnect requests, at one time. The ability to perform multiple tasks at any given time (e.g., reading from one drive while writing to another) is critical, especially as applications become more complex and requirements become more stringent. For multiple-processing capabilities from ATA drives, users can integrate ATA-to-SCSI converters.
  • Reliability: SCSI drives do cyclical redundancy checking (CRC) throughout the interface and the media. In contrast, CRC in ATA drives is limited to the media. This results in a slightly better error rate for SCSI devices, versus ATA (1 x 10-15 vs. 1 x 10-14). However, for improved reliability, users can assemble ATA drives in various RAID configurations.
  • Pricing: Another important point to consider is the role of pricing in ATA's climb up the application scale. A typical SCSI drive is two to three times more expensive than comparable ATA devices. However, as noted above, Seagate this month plans to announce high-end SCSI drives at ATA prices. Just what affect-if any-these products will have on ATA drives-or competitive SCSI devices-is uncertain. Similarly, will ATA be able to maintain its pricing advantage going forward?

"Pricing is going to be determined by the volume [of drives]," says Quantum's McGarrah. "Let's say someone comes out with a 15,000rpm ATA drive. That doesn't mean there is going to continue to be a significant price difference between 15,000rpm SCSI and 15,000rpm ATA drives."

"There are certain efficiencies we are able to achieve with ATA drives," explains Richard Van Dyke, senior manager of product marketing, Maxtor. These efficiencies translate into lower prices for consumers, assuming volumes are maintained. The equation, however, presumes that SCSI pricing will remain at or near current levels.

When all is said and done, pricing is clearly the key motivating factor among users to choose ATA drives over SCSI devices. "The price differential is so attractive that users are prepared to make sacrifices," says Mike Chenery, vice president, advanced product, Fujitsu.

"If you can get the performance you need to satisfy your requirements, then ATA should be considered," adds Shawn Hook, manager of product marketing for Seagate's enterprise storage group.

However, as requirements become more complex and drive numbers increase, SCSI-or Fibre Channel-may be the better choice.

Opening photo courtesy of Seagate Technology.

Fibre Channel, rpm update

By all accounts, Fibre Channel adoption has been much slower than anticipated. This is certainly true at the hard-disk-drive level. By year-end, Fibre Channel drives are projected to account for just 6% of high-end drive shipment and 0% of desktop units, according to IDC estimates.

"The big advantage of Fibre Channel is its distance capabilities, and out the back-end of a hard drive you don't need that distance," says IDC's Dave Reinsel.

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Hitachi, IBM, and market leader Seagate are all manufacturing Fibre Channel drives; Quantum is not.

rpm report

Seagate remains the sole manufacturer of 15,000rpm disk drives, although other vendors are expected to follow suit by mid-2001. In introducing the Cheetah X15 drive last quarter, Seagate has some clear advantages. (For more information, see, September 2000, p. 64: "Seagate's X15 puts the spin on performance.")

"It gives them the opportunity to drive home their current role as high-end market leader, as well as the chance to work out all the wrinkles with the technology well before everyone else," explains Reinsel.

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Nonetheless, the transition to 15,000rpm is expected to be slow-significantly slower, in fact, than the transition from 7,200rpm to 10,000rpm drives. The price premium of 15,000rpm technology is largely to blame. In going from 10,000rpm to 15,000rpm, the media size is reduced from 3.5 inches to 2.5 inches, which means more platters are needed to achieve the same capacity. As platter numbers increase, so too do drive prices.

"Does the performance boost justify the up-tick in price?" asks Reinsel. "The answer is basically no, not at this point."

According to IDC estimates, Seagate will ship some 100,000 15,000rpm drives this year. These drives will account for about 0.4% of high-end drive shipments in 2000 (vs. 65.7% and 34.0% for 10,000rpm and 7,000rpm drives, respectively). On the desktop, 5,400rpm accounted for 70.0% of shipments, 7,200rpm for 23.0%. Fujitsu, IBM, Hitachi, Quantum, and Seagate manufacture 10,000rpm drives.

Make way for serial ATA

At the Intel Developer Forum this summer, APT, Intel, Seagate, and Vitesse showcased the first serial ATA disk drive. The device featured a blistering 1.5Gbps, or 150MBps, bandwidth-a 50% increase over comparable parallel Ultra ATA/100 devices. The product roadmap calls for at least two more generations of serial interfaces, with a doubling of throughput each generation.

Unlike its parallel predecessors, Serial ATA is a point-to-point protocol, which connects each drive to the IDE controller for improved scalability. The interface features fewer pins than parallel designs (6/8 vs. 40), reducing overall drive cost and improving device reliability. Serial ATA is backward compatible with parallel ATA and may support hot plugging.

The interface is being jointly developed by APT Technologies, Dell, IBM, Intel, Maxtor, Seagate, and Quantum, and is supported by a 40-member working group, representing silicon design, cable/connector, storage, and system vendors industry-wide (see chart).

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A final spec is expected this fall, with product delivery within 12 to 18 months.

SCSI functionality at ATA pricing

Start-up Alcita Technologies last month announced IDEplex2, an ATA PCI card that acts as an ATA-to-SCSI converter in Ultra SCSI JBOD or tower environments. Support for low-voltage differential 160 (LVD 160) SCSI JBOD and RAID 0,1, and 5 is expected within the next two months.

Essentially, the converter enables users to connect up to eight high-capacity, low-cost ATA hard drives, CD-ROM, or DVD-ROM drives into peripheral tower or rack configurations via an external ATA PCI card. The card connects to a SCSI bus on the host, and appears as a single device ID on the bus. The card supports most ATA drives and SCSI host bus adapters.

For example, users will be able to connect up to eight 62GB ATA drives in a RAID configuration, providing more than 0.5TB of storage for $2,000 to $3,000, compared to $8,000 to $10,000 for a lower-capacity SCSI solution, says Steven Wolsky, vice president of operations at Alcita. And the configuration is not limited by the number of on-line devices (two per bus), cable lengths (19 inches), or processing (one transaction at a time).

"We solved all that by making it ATA into the card and SCSI on the way out," explains Wolsky. "This gives users the benefits of both SCSI and ATA-at ATA prices." Cable lengths are extended to 6m, up to eight drives can be supported per bus, and multiple transactions can be processed concurrently.

However, unlike controller cards from vendors such as 3Ware and Promise Technology, IDEplex2 goes inside the storage device, not the server, which means that drive count is not limited to the space in a given server, but to the eight channels on the bus, according to Wolsky. And because the card is external, up to seven towers, each with eight drives, can be configured together.

Target applications include large data farms, imaging, video storage, near-line storage, and high-performance backup.

Serial ATA Working Group Founders:
APT Technologies

American Megatrends
Bitzbltz Communications
Bus Probes
Circuit Assembly
Cirrus Logic
CMD Technology
Conner Technology
DCM Technologies
FCI Electronics/Berg
Innotec Design
Marvell Technology
Oxford Semiconductor
Pacific Digital
Promise Technology
Silicon Image
St. Microelectronics
Standard Microsystems
Texas Instruments
Via Systems
Via Technologies
Western Digital

This article was originally published on October 01, 2000