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Square One: eSATA Hard Drives

October 1, 2008
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External SATA (eSATA) drives can provide better speed than either USB 2.0 or FireWire hard drives. The Seagate FreeAgent Xtreme (above) includes all three types of connectors on the rear panel (right).

External SATA (eSATA) drives can provide better speed than either USB 2.0 or FireWire hard drives. The Seagate FreeAgent Xtreme (above) includes all three types of connectors on the rear panel (right).

Modern musicians are always looking for larger, faster, and more-convenient data storage. The current trend in mobile storage is eSATA, the external version of the SATA (Serial AT Attachment) standard. As its name suggests, this standard is related to the ATA/IDE specification, under which most internal drives have operated since the late 1980s. SATA drives are increasingly popular with PC users and have been standard on Mac desktops since the first G5s.

External Influence

Almost as soon as SATA drives first appeared, people started adapting them for external use, but the eSATA specification wasn't formalized until 2004. The official spec includes several optimizations for external use. A proper eSATA cable has an extra layer of shielding for greater protection from electromagnetic interference. In an effort to guard against electrostatic discharge upon insertion, the metal contacts are set deeper into the connector. To be sure that internal and external devices won't be mistaken for one another, the eSATA connector doesn't have the L-shaped insertion guide that characterizes the internal SATA connector.

The performance of eSATA outstrips its competition by a wide margin. USB 2.0 offers maximum data transfer at 480 Mbps (megabits per second), and FireWire 800 (IEEE-1394b) goes up to 800 Mbps. eSATA comes in two flavors: 1.5 Gbps and 3 Gbps. If you see a reference to SATA II, it probably means the 3 Gbps variety, but the name SATA II is incorrect.

If you divide 1,500 Mbps by 8 bits per byte, you would expect to get 187.5 MBps (megabytes per second). However, since SATA uses 8-bit-to-10-bit encoding (meaning that each set of 8 bits is mapped to 10 bits for technical reasons), SATA 1.5 Gbps provides “only” 150 MBps. If you compare that with USB 2.0's 60 MBps and FireWire 800's 100 MBps, eSATA's appeal to electronic musicians is immediately apparent.

Serial Killer

In the demanding world of external audio drives, USB has met with mixed success. Some people report great results using them with USB 2.0, but Digidesign specifically recommends against external audio drives for its Pro Tools systems. Although no other DAW manufacturer has issued a similar warning, that still represents a significant downside for USB. Though Digidesign has not yet officially qualified eSATA drives, the widespread consensus of Pro Tools users is that the drives are perfectly compatible.

FireWire drives are more universally accepted than USB, but there have been enough reports of fried controller chips when hot-swapping that several informed sources have been advising against the practice. Having had friends lose hardware this way, I always power down FireWire drives (if not the computer itself) before disconnecting them. To date, eSATA's hot-swap capabilities seem to be more robust.

Because few, if any, computers currently ship with eSATA ports, various devices are available to provide such connections. CardBus and ExpressCard solutions are available for notebooks, and PCI cards are available for desktops. SATA-to-eSATA extenders are available from a couple of sources (for example, from Sonnet [sonnettech.com]) that take advantage of two unused SATA connections on MacPro motherboards. But because they are merely adapters and not host bus interfaces, they are not fully eSATA compliant. Most significantly, they don't support hot-swapping.

When using a SATA controller, make sure your BIOS is running in AHCI (Advanced Host Controller Interface) mode instead of PATA (Parallel ATA) compatibility mode. AHCI is necessary to support hot-swapping, and it enables a feature called Native Command Queuing (NCQ). NCQ allows the drive to decide the best order in which to execute incoming requests, reducing inefficiencies in drives that support it.

Short Shrift

Two aspects of the eSATA specification come up short. First, the recommended maximum cable length is only 2 meters. Though this is fine for a single drive sitting on a desk, it complicates matters in a studio, where drives are commonly placed farther away to keep them quiet. Second, eSATA does not provide power to drives, making it slightly less convenient for remote recording.

The only constant in technology is change, and SATA-IO (sata-io.org), which oversees the SATA spec, has recently approved a 6 Gbps standard. With USB 3.0 promising 4.8 Gbps, and with 3.2 Gbps and 6.4 Gbps FireWire standards being developed, we're sure to revisit this subject periodically.


Brian Smithers is department chair of workstations at Full Sail University in Winter Park, Florida.

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