|Digital content professionals have unique requirements for data 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. So to get the most bang for their buck—at least in terms of storage capacity—they often turn to disk arrays based on Fibre Channel or SCSI (Small Computer System Interface) connections for use in stand-alone or networked storage systems.
Now there's a new breed of disk storage based on the Serial ATA (Advanced Technology Attachment) interface that is expected to provide a lower-cost storage alternative to arrays based on Fibre Channel or SCSI drives. Serial ATA (or SATA) disk arrays, which typically hold about 250GB per drive, promise performance levels that are "good enough" for most digital content applications, including animation, 3D rendering, nonlinear video editing, and a variety of other rich-media applications.
Choosing the right disk 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 percent less for SATA disk arrays than for high-end SCSI or Fibre Channel arrays, assuming equal capacity. Indeed, for relatively small configurations (of less than, say, 4TB), the cost differential could be approximately 30 percent, she explains, while for high-capacity configurations (requiring upward of 12TB), the price difference could reach 50 percent.
In fact, at this month's NAB show, storage vendor Ciprico will introduce a disk array based on Serial ATA that the company claims provides Fibre Channel performance at half the price. Ciprico, which also sells Fibre Channel arrays, will be demonstrating its FibreStore 2212A SATA disk array priced at $17,100 for a 1.5TB entry-level version. Target applications for Ciprico's SATA disk systems, according to the company, include nonlinear editing and film scanning.
|IT professionals already are planning to make the transition to disk arrays based on the Serial ATA interface.
How popular will SATA disk drives be? According to IDC analyst Dave Reinsel, SATA will be the dominant disk drive interface for desktop platforms within two years. In fact, he predicts that shipments will skyrocket from 2.5 million units last year to some 124 million units in 2005, which represents a compound annual growth rate of more than 400 percent.
The surge in popularity of SATA drives in non-desktop systems is expected to be robust as well. Reinsel estimates that shipments of "enterprise-class" SATA drives will soar from a half million units last year to 3.6 million units in 2005.
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 input/output streams you're transferring. For random I/O streams with relatively small blocks of data, Serial ATA disk arrays almost always will be slower than Fibre Channel or high-end SCSI arrays. However, if you're inputting or outputting large blocks of data at a time (as many studios do when streaming video data, for example), a SATA disk subsystem may be almost as fast as a Fibre Channel or SCSI disk array.
"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, which recently began shipping SATA disk arrays based on technology from LSI Logic Storage Systems. Early users of SGI's SATA disk arrays include Efilm and Pacific Title & Art Studio, both of which are using the arrays for near on-line, or "nearline," archiving, which requires faster data-access speeds than are available with off-line tape-archiving systems.
"There's a huge demand for Serial ATA in graphics-intensive environments, driven mainly by SATA's low cost," says Farney. But, he cautions, while Serial ATA RAID (Redundant Array of Inexpensive Disks) can fulfill the bandwidth requirements of most studio applications, if you need the highest bandwidth and/or you have a lot of users (say, 20 or more) who are simultaneously accessing the same storage subsystem, you may need to go with Fibre Channel RAID arrays.
Of course, performance is highly application-dependent and will vary according to factors such as the size of the data blocks being transferred, sequential versus random access, standard-definition versus high-definition video, and so on. But vendors that sell storage systems with a variety of disk interfaces (for example, 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, which discontinued its SCSI-based disk arrays about four years ago.
Similarly, SGI's Farney says, "In general, SATA doesn't have the performance of Fibre Channel. However, in media environments, which are often characterized by very large, sequential reads and writes, SATA delivers almost as much performance as Fibre Channel."
Because of their lineage in desktop platforms, SATA disk drives are often characterized as being less reliable than Fibre Channel or SCSI drives, which were developed for server, rather than desktop, platforms. However, vendors that have experience with all the major disk drive interfaces say that there is little difference in reliability among the various interfaces, at least in environments that do not require constant storage access. "Even with our Parallel ATA systems [the predecessor to systems based on Serial ATA, also known as IDE, or Integrated Drive Electronics], the drive failure rate was about the same as SCSI and Fibre Channel," says Johnson. "Serial ATA blurs the line between desktop-quality drives and so-called 'enterprise-class' drives."
While Serial ATA is creating a great deal 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 NAB.
Mike Anderson, Huge Systems' chief technology officer, points out that the Ultra320 SCSI product may be best suited for studios working with high-definition video. Conversely, he says that single-channel Fibre Channel disk arrays, which feature one connection into the disk subsystem, typically can't handle HD video. Although Fibre Channel is rated at a theoretical maximum transfer rate of 200MBps, users usually realize only about 140 to 150MBps. You can add channels to the disk subsystem to boost throughput rates, he explains, but that significantly increases the price of the array.
Anderson says that Huge Systems' five-drive Ultra320 SCSI disk array can achieve rates of 220MBps, which is enough performance for HD video streams. The system can record and play back high-quality video, including 1080i HD at 10 bits, or it 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," says Anderson, "which will make them more appealing for 24x7 operation."
Although some vendors pitch Serial ATA disk systems as primary on-line storage devices, SATA is also a good fit as a secondary, or nearline, storage device. In these scenarios, the SATA disk system sits between primary storage arrays (for example, 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 Farney. He adds that some large studios are starting to implement "tiered" storage architectures, whereby 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.
Whether you use it for primary or secondary storage, disk subsystems based on Serial ATA technology are good news for budget-constrained production facilities.
Dave Simpson is editor-in-chief of InfoStor magazine. He can be reached at firstname.lastname@example.org