ATA/SATA drives fitting bigger niches

The economics of enterprise storage are on the verge of a significant alteration, thanks to the Advanced Technology Attachment (ATA) disk drives and, more specifically, a new generation of serial ATA (SATA) drives that have been shipping since early last year. It remains to be seen whether the low-cost, PC-class disk drives actually replace server-class SCSI and Fibre Channel (FC) drives for enterprise production storage, although at least one vendor is trying to push the technology to that level.

"ATA already is being used in massive volumes," says John Monroe, research vice president at Gartner. "It has adequate speed, an excellent cost, and its reliability is good enough." Monroe expects SATA drives to replace ATA drives within two years. This replacement, however, will appear on the desktop and for light duty-cycle usage, in which the drive is not continually engaged in writing and reading.

In theory, disk arrays - and particularly RAID arrays - built using ATA and SATA disk drives will enable storage managers to lower the cost of disk capacity by replacing more costly SCSI drives with less costly ATA/SATA drives wherever appropriate.

Initially, applications ripe for this low-cost storage are characterized by infrequent read/write activity, such as file serving applications, content delivery, archiving, bulk storage and business intelligence. Some proponents, however, suggest that even mission-critical application storage characterized by constant read/write activity will benefit from SATA disk drive technology when combined with RAID to ensure data protection in the event of a disk drive failure.

The ATA interface, formerly IDE (Integrated Drive Electronics), has been the PC disk drive interface standard for well over a decade and serves as the foundation for PC-class disk drives. ATA sends data in parallel and delivers acceptable performance and capacity at a low price, achieved through mass-market economies of scale as well as the use of less rugged mechanical components. SATA sends data serially, which allows for the use of a slim, round, flexible cable that supports distances up to one meter, about double the distance for an ATA drive. SATA uses the same lightweight mechanical components as ATA but also allows for hot swapping of drives, which ATA does not.

Server-class drives: Higher performance, higher price

SCSI and Fibre Channel drives, on the other hand, are aimed at server environments and deliver a much higher level of reliability, dubbed "server-class." SCSI/FC drives offer higher performance and support heavy usage characterized by nearly continuous read/write activity. SCSI/FC drives use sturdier mechanical components to ensure greater reliability, which comes at a higher price.

The future of SATA is not so clear as a replacement for SCSI/FC in heavy duty-cycle enterprise situations. The big appeal of SATA is the low cost and large capacity of the disk drives. On a cost-per-gigabyte basis, ATA/SATA can't be beat. The difference in price between ATA/SATA and SCSI/FC is at least 50% on a per-gigabyte basis, says Peter Kastner, executive vice president at Aberdeen Group in Boston.

However, when it comes to storage for mission-critical production applications, the good-enough reliability of SATA may not be sufficient, and efforts to boost the ruggedness of SATA drives may be counter-productive. "If you take a SATA drive and put in enterprise-class components and spin it at higher speeds and go through all the testing, then you will increase the cost of the drive," notes Monroe. SCSI/FC drives already sport the rugged mechanical components and higher RPM rates required for enterprise usage.

A SAN that makes sense

Rather than replace SCSI in its primary production application, LocatePlus Holding Corp. in Beverly, Mass., turned to ATA to augment its enterprise storage. The company collects massive amounts of data online, which it provides to police departments, government agencies and lawyers for investigative purposes. Until just recently, it assembled its own disk arrays using ATA drives. Although it really wanted a SAN, "the cost was prohibitive," says Jon Latorella, LocatePlus CEO.

When EMC recently introduced a CLARiiON midrange system that combines ATA and FC drives in the same box, the result was "a competitively priced SAN solution that made sense to us," Latorella continues. The company took 45 TB of mixed ATA/FC storage. It earmarks about 7 TB of Fibre Channel capacity for its primary production storage. The rest is ATA capacity used for data staging, a process by which the company organizes massive volumes of ASCII data for conversion into SQL tables before making it available as production data. The price tag was one-third the cost of what an entirely FC system would be, Latorella notes.

The distinction, however, between PC-class and server-class drives as far as enterprise storage goes is blurring. "IT managers are realizing that much of their enterprise storage isn't very active. There is a lot of old e-mail or old CAD drawings," says Kastner, referring to data that is accessed occasionally but does not require costly, highly reliable, highly available, heavy duty-cycle storage. "They can put that data on ATA drives and save money," Kastner notes.

Looking ahead at the implications of legislation like Sarbanes-Oxley, which will require large amounts of data to be readily accessible but lightly accessed, the need for large amounts of light duty-cycle storage will only increase. You don't need SCSI/FC for this.

Drive vendors are rushing to position their PC-class products to meet such enterprise storage needs. "SATA plays in the low end of enterprise storage," says Eric Schou, senior product manager at Maxtor, which offers both server-class SCSI and PC-class ATA disk drives. Maxtor ATA drives come with a one-million-hour MTBF (Mean Time Between Failure) rating and a three-year warranty. Its SCSI server-class drives have a 1.2-million-hour MTBF rating and a five-year warranty. Maxtor could boost the ruggedness of its ATA drive, but then those ATA/SATA drives would lose their cost advantage.

Vendor strategies

Instead, Schou suggests using ATA drives for light duty-cycle applications where the drive reads/writes 10% to 20% of the time and for low-cost bulk storage. If organizations want to run the lightweight ATA drives in a heavy duty-cycle environment, however, they should take advantage of the low cost to mirror the storage, which will reduce the risk of data loss due to disk drive failure.

Western Digital is taking a different approach. Last year, it introduced the 36.7GB Raptor, which it describes as an enterprise-class SATA drive. Unlike standard ATA/SATA drives, it offers specifications that rival SCSI drives: 10,000 RPM rotational disk speed and heavy-duty internal components, such as high-end bearings. It comes with a 1.2-million-hour MTBF rating and a five-year warranty. The price tag, although higher than conventional ATA/SATA, still comes out about 30% less than SCSI, according to the company.

Western Digital was the first major drive maker to announce a rugged enterprise SATA drive. Other manufacturers, like Maxtor and Seagate Technologies, say they don't intend to make such drives, at least for now.

Desktop dominance?

Industry analysts don't see SATA making inroads into primary enterprise storage anytime soon. Instead, they expect SATA to take over the desktop and selected enterprise storage tasks, such as bulk storage, archiving, content serving and light duty-cycle applications. Within a few years, "one-third of enterprise storage will be SATA, but it will be at the low end," predicts Gartner's Monroe. The remaining two-thirds will be Fibre Channel, SCSI and SAS (serial-attached SCSI, expected to first appear in mid-2004).

"ATA/SATA creates a new service level based on the performance-cost tradeoff," says Chuck Hollis, vice president at EMC Corp. "With a cost and speed lower than SCSI/FC but higher than tape, it fits nicely between tape and Fibre Channel," he concludes. As such, ATA/SATA gives storage managers a new option when faced with a disk or tape decision.

Alan Radding is a business and technology writer. He can be reached at alan@radding.net.

Copyright © 2004 IDG Communications, Inc.

  
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