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eSATA Raises the Price-Performance Bar

My columns about various external storage technologies have generated a lot of reader response. It seems that there's still an unfilled need at the entry and departmental levels for inexpensive, easy-to-use, reliable storage that can grow with the needs of the user base. The easy availability of USB 2.0 and IEEE 1394 (aka FireWire) attached devices has addressed much of the market need, but a significant percentage of readers who have contacted me seek solutions that provide better performance and greater capacities than the current external storage technologies provide.

Although some of these readers have been willing to adopt external SCSI enclosures and others have gone to entry-level NAS and SAN systems, the majority are looking for something they can attach to a special-purpose desktop (such as an image-editing or video workstation) or a departmental or entry-level server. They're willing to spend more than the cost of current USB and IEEE 1394 enclosures, but they don't want to make the jump all the way to the cost of SCSI.

For these users, the answer might just be found in the form of External SATA (eSATA) devices. eSATA is an extension of the Serial ATA (SATA) standard to external devices and is designed to compete directly with USB 2.0 and IEEE 1394 storage devices. eSATA's biggest advantage is that it provides full SATA bandwidth (currently 1.5Gbps, but soon to be 3Gbps) versus the 480Mbps of USB 2.0 and 400Mbps of IEEE 1394. Because eSATA uses standard SATA drive technology, the planned increases in performance to the SATA standard, such as the soon-to-be-released 3Gbps drives, mean that the external-drive performance will continue to grow along the growth path to 6Gbps as outlined in the Serial ATA International Organization's (SATA-IO's) SATA storage roadmap. (See for the standards and growth plans of the SATA standards body.) Additionally, the eSATA standard specifies a default hot-swap capability, which isn't found in USB 2.0 and IEEE 1394 devices.

Although the apparent performance improvement of eSATA over USB 2.0 and IEEE 1394 external drives is more than 300 percent, even the SATA-IO tests show that the improvement isn't quite as large as it seems. At best, the burst transfer rate can be triple the competing standards, taking advantage of the raw interface speed. However, in more common read and write tests using 64K blocks, performance improvements range from 30 percent (in read tests) to 100 percent (in write tests). This testing was done with drives that have the current 1.5Gbps interface; Seagate Technology announced last week that it will be ship its Barracuda 7200.9 3Gbps SATA drive, which will be eSATA enabled, before the end of the year. Given double the raw interface performance, the actual performance benefit to end users, especially when compared with existing external storage technologies, will be significant.

Cabling for eSATA allows lengths of up to 2 meters, designed specifically to let computers sit on the floor and enclosures sit on the desktop. Motherboards with eSATA connectors are starting to appear. For older systems, host bus adapters (HBAs) are available to provide additional SATA ports with external eSATA connectors, or alternatively you can use simple brackets and connectors to allow internal SATA ports to be routed externally. HBAs will also let current SATA-equipped computers support the new 3Gbps drives as they become available.

Various vendors currently offer eSATA enclosures that provide capacities up to 2TB with the current-generation eSATA drives. (When buying eSATA products, make sure that this type of enclosure meets the eSATA standard and isn't one of the proprietary devices that appeared before the eSATA standard was finalized.) Prices for fully configured eSATA products hover around the $3000 range, which makes eSATA a difficult combination to beat in terms of price and performance.

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