Serial ATA means low-cost storage

For many graphics applications, disk arrays based on SATA disk drives may provide as much performance as Fibre Channel disk arrays—at half the cost.

By Dave Simpson

Digital content professionals have unique requirements when it comes to data and content storage. They need extremely high capacity and as much speed as they can afford. Unfortunately, most studios operate under tight budgets when it comes to capital expenditures for computing equipment.

A relatively new disk drive interface—called Serial ATA, or SATA—promises to solve those problems by providing significantly lower-cost storage subsystems than those based on disk interfaces such as Fibre Channel and SCSI, at performance levels that are "good enough" for most digital content applications, including animation, 3D rendering, non-linear video editing, and a variety of other rich media applications.

Choosing the right storage system for your environment comes down to a tradeoff between cost and performance. Although pricing on disk arrays varies widely, Charlotte Rancourt, a senior analyst with International Data Corp. (IDC), says that end users can expect to pay 30% to 50% less for SATA disk arrays versus high-end SCSI or Fibre Channel arrays, assuming equal capacity. For high-capacity configurations (greater than 2TB), the cost differential could be close to 50%, while smaller configurations (less than 4TB) would come closer to a 30% price difference.

At next month's NAB show, Ciprico will introduce a disk array based on Serial ATA that the company claims provides Fibre Channel performance at half the price. (Ciprico also sells Fibre Channel disk arrays.) The company's FibreSTORE 2212A disk array is priced at $17,100 for a 1.5TB entry-level version. Target applications for Ciprico's SATA disk systems include non-linear editing and film scanning.

Also at NAB, Ciprico will showcase its DiMeda (Digital Media Appliance) 1700, a network-attached storage (NAS) file server based on Serial ATA drives. (The DiMeda 1700 with SATA drives was introduced at last September's International Broadcasters Association show, where it won a STAR "best-of-show" award.)

(For a review of other recent SATA-related product announcements, see the New Products section in this issue, p. 49.)

As evidence of how popular SATA disk drives will be, IDC analyst Dave Reinsel predicts that SATA will be the dominant disk drive interface for desktop platforms within two years, with shipments skyrocketing from 2.5 million units last year to more than 51 million units this year, topping 124 million units in 2005—a compound annual growth rate of 406%.

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The surge in popularity of SATA drives in non-desktop systems is expected to be almost as stunning. Reinsel predicts that shipments of "enterprise-class" SATA drives will go from half a million units last year to two million units this year and 3.6 million units in 2005 (see charts).

In addition to low cost, Serial ATA disk drives hold a lot of capacity per drive—250GB in most cases—relative to SCSI and Fibre Channel disk drives.

Performance factors

On paper, Serial ATA is not as fast as Fibre Channel or high-end SCSI disk systems, but its performance may be sufficient in many media environments. SATA is rated at 150MBps, compared to 320MBps for Ultra320 SCSI and 200MBps for Fibre Channel. However, those are only theoretical maximum ("burst") throughput ratings. Your mileage will vary.

Actual performance depends largely on the type of I/O (input/output) streams you're transferring. For random I/O with relatively small blocks of data, Serial ATA disk arrays will almost always be slower than Fibre Channel or high-end SCSI arrays. However, if you're transferring sequential I/Os in large blocks (for example, streaming video), the performance of a SATA disk subsystem may be almost as fast as a Fibre Channel or SCSI disk array. Fortunately, the latter scenario describes the I/O activity at most studios.

"Media environments are often characterized by very large, sequential reads and writes, and in those environments SATA delivers almost as much performance as Fibre Channel," says Jim Farney, senior marketing manager at SGI (and the owner of a post-production facility—Pacific Video Resources, in San Francisco—for more than 20 years before he joined SGI).

"There's a huge demand for Serial ATA in graphics-intensive environments, driven mainly by SATA's low cost," says Farney. (SGI started shipping SATA disk arrays, which are based on systems from LSI Logic Storage Systems, in the fourth quarter of last year. Early users of SGI's SATA disk arrays include EFILM and Pacific Title & Art Studio, both of which are using the arrays for nearline archiving.)

Although Farney says that Serial ATA RAID arrays can fulfill the bandwidth requirements of most studio applications, if you need the highest bandwidth and/or you have a lot (20 or more) of users simultaneously accessing the same storage subsystem, you may need to go with Fibre Channel RAID arrays.

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Of course, performance is very application-dependent and varies according to factors such as the size of the blocks being transferred, sequential vs. random access, and standard-definition vs. high-definition video, etc. But vendors that sell storage systems with a variety of disk interfaces (e.g., SATA, Fibre Channel, and SCSI) are surprisingly consistent in their performance evaluations.

"Our 12-drive SATA array is approximately performance-equivalent to our 10-drive Fibre Channel array—at about half the price," says Gerry Johnson, senior product manager at Ciprico. (Ciprico discontinued its SCSI-based disk arrays about four years ago.)

Reliability issues

Because of its lineage as an interface for desktop platforms, SATA disk drives are often characterized as being less reliable than Fibre Channel or SCSI drives. However, vendors that have experience with all of the major disk drive interfaces say that, at least in environments that do not require constant storage access, there may be little difference in reliability among the various interfaces. "Even with our Parallel ATA [the predecessor to Serial ATA, also known as IDE] disk subsystems the drive failure rate was about the same as SCSI and Fibre Channel," says Ciprico's Johnson. "Serial ATA blurs the lines between desktop-quality drives and so-called 'enterprise-class' drives."

While Serial ATA is creating a lot of buzz in graphics-intensive environments, some storage vendors—and end users—are sticking with other disk interfaces, at least for now.

For example, Huge Systems, a storage vendor that specializes in video and rich media markets, will showcase its line of SCSI disk arrays, including a new system based on the Ultra320 SCSI disk interface, at next month's NAB show.

Mike Anderson, Huge Systems' CTO, points out that Ultra320 SCSI may be the best fit for studios working with high-definition video. Anderson says that single-channel Fibre Channel disk arrays typically can't handle high-definition video with a single link.

Although Fibre Channel is rated at a theoretical maximum transfer rate of 200MBps, users typically realize only about 140MBps to 150MBps, which isn't fast enough for high-definition video applications, according to Anderson. (You can add channels to the disk subsystem to boost throughput rates, but that increases the price of the disk array significantly.)

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Anderson says that Huge Systems' five-drive Ultra320 SCSI disk array can handle 220MBps, which is more than enough performance for high-definition video streams. The system can record and play back high-quality video (including 1080i HD at 10 bits) or can handle up to six uncompressed standard-definition video streams.

Despite its current emphasis on SCSI disk arrays, Huge Systems plans to introduce a disk array based on Serial ATA drives in the third quarter. "The next generation of SATA drives will have better reliability, which will make them more appealing for 24x7 operation," says Anderson.

Although some vendors pitch Serial ATA disk systems as primary (online) storage devices, SATA is also a good fit as a secondary storage device. In these scenarios, the SATA disk system sits between primary storage arrays (e.g., high-performance Fibre Channel arrays) and tape systems that are used for archiving content. Essentially, the secondary disk array allows users to "park" content on an inexpensive storage medium. The SATA disk subsystem is less expensive than the primary disk systems and is much faster than tape libraries for content retrieval.

"A film with a lot of special effects can be 30TB, or much more, and it doesn't make economic sense to put that much capacity on expensive Fibre Channel arrays," says SGI's Farney. He adds that some large studios are starting to implement "tiered" storage architectures where, once a film is completed, the content is moved to Serial ATA arrays for subsequent access and then to tape for long-term archiving.

In a related trend, some studios are using Serial ATA disk arrays to replace slow-access tape libraries as backup devices. SATA disk arrays are almost as inexpensive as tape libraries, but they provide much faster access times.

"There's a big trend toward ATA and Serial ATA in studio environments, but mainly as secondary storage," says Jay Krone, director of CLARiiON platforms marketing at EMC. "Digital content professionals can keep massive amounts of content 'nearline' or archived. ATA is also good in applications such as streaming video and video-on-demand."

This article was originally published on March 01, 2004