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Explainer: SATA reduces storage costs

Explainer: SATA reduces storage costs

Serial Advanced Technology Attachment is an emerging standard electronic interface technology. SATA promises to exceed its predecessor, Parallel ATA, by delivering better performance at a fraction of the cost of traditional storage technology such as SCSI or Fibre Channel.

As the name suggests, SATA is simply a serial link or interface standard used to control and transfer data and information from a server or storage appliance to a client application. SATA is used to connect storage devices such as hard disk drives to motherboards and can increase system performance, improve efficiency and reduce development costs greatly.

Parallels and differences

To understand the benefits of SATA, a closer examination of Parallel ATA is required. Parallel ATA, a hard disk drive technology based on the Integrated Drive Electronics (IDE) interface standard, is used for the transfer and communication of data between a computer motherboard's bus and disk storage devices.

Many low-end network-attached-"storage (NAS) devices use Parallel ATA drives because of the cost benefits. Moreover, there are numerous high-bandwidth applications such as backup and recovery, video surveillance, video manipulation and near-line storage that use disks instead of tape.

The configuration of storage devices using SATA is much simpler than its predecessor, thanks to its sleeker form factor. SATA uses longer, thinner cables than Parallel ATA, which uses bulky, fragile and short cables. SATA also uses a seven-pin data connector as opposed to the 40-pin found in Parallel ATA.

Bulky cables connected to disk drives are more difficult to set up, block airflow and induce heat, all of which affect the overall performance and stability of hardware systems. SATA's cables are much simpler to route and install, and the compact nature provides additional space on motherboards and disk drives.

SATA also uses low-voltage differential signaling, which is consistent with low power and cooling requirements. Signal voltages have been lowered from 5 volts on Parallel ATA to a mere 0.7 volts on SATA. This enables lower power handling on a disk drive and reduces the size of a switch controller.

The interface technology uses 8B/10B encoding, a method for encoding eight-bit data bytes to 10-bit transmission characters. Using serial technology with eight-/10-bit encoding improves overall transmission and completely bypasses the parallel transmission problems. This high-data-integrity scheme provides the essential embedded timing and significant data-integrity checking provisions that high-speed transmissions require.

By using point-to-point topology as opposed to a bus-based architecture found predominantly in Parallel ATA or SCSI technologies, SATA can deliver full bandwidth to each connected drive, thereby improving overall performance. With a road map consisting of three generations of increased data-transfer rates at 150M, 300M and 600M bit/sec device burst rates, SATA is poised for 10 years of steady but healthy growth, according to the Serial ATA Working Group. The new standard also is backward-compatible, making it simpler to convert from Serial to Parallel formats and vice versa, and also should speed the adoption rate of SATA.

Future deployment

With flexible thin cables, hot-plug connectors, improved data reliability and protection, along with full software compatibility, SATA will create huge market opportunities for inexpensive network storage products. Many disk drive and chip manufacturers have announced products supporting SATA, and there has been widespread industry support through the Serial ATA Working Group, comprising more than 80 vendors.

Currently, SATA costs about 15 percent more than Parallel ATA, but the gap is closing fast, and SATA is expected to be on par with today's Parallel ATA in the near future.

- Cleland is a technical marketing manager for 3ware Inc. He can be reached at scleland@3ware.com


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