Storage advances to boost throughput

New storage connectivity technology is on the horizon that promises faster performance, greater scalability and more flexibility for companies of all sizes.

The two technologies expected to take center stage early next year are Serial Advanced Technology Attachment (SATA) and Serial Attached SCSI (SAS). SATA and SAS are point-to-point connections for attaching servers to internal or closely located storage. The SATA and SAS connections consist of a controller, which fits in a PCI, PCI-X or PCI Express slot in the PC or server and attaches to ATA or SCSI drives.

Fujitsu, Seagate and Maxtor are expected to introduce SATA drives this year; IBM, Dell and Hewlett-Packard will introduce PCs and servers that integrate the SATA specification early next year. SAS products will start to appear in 2004, vendors say.

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New storage connectivity technology is on the horizon that promises faster performance, greater scalability and more flexibility for companies of all sizes.

The two technologies expected to take center stage early next year are Serial Advanced Technology Attachment (SATA) and Serial Attached SCSI (SAS). SATA and SAS are point-to-point connections for attaching servers to internal or closely located storage. The SATA and SAS connections consist of a controller, which fits in a PCI, PCI-X or PCI Express slot in the PC or server and attaches to ATA or SCSI drives.

Fujitsu, Seagate and Maxtor are expected to introduce SATA drives this year; IBM, Dell and Hewlett-Packard will introduce PCs and servers that integrate the SATA specification early next year. SAS products will start to appear in 2004, vendors say.

Analysts say they expect SATA and SAS controllers and drives to replace the current parallel ATA and parallel SCSI used now in servers and workstations. They say SATA will be used in entry-level to midrange servers where cost is an issue; whereas SAS will be implemented in high-end and midrange servers running business-critical data center applications.

Gartner expects the number of ATA/SATA drives to exceed 9.2 million in 2006 from 2.4 million drives this year. IDC estimates that SATA drives will represent nearly 100% of all ATAs shipped in 2005.

Sated with SATA

The SATA connection is designed for reliable operation in servers that are hosting static Web pages or running file/print applications and to replace parallel ATA implementations. Parallel ATA, analysts say, has reached the end of its capabilities.

The technology was introduced in the 1980s and is the standard storage interface for PCs and servers. It is a relatively simple interface that performs as fast as 66M byte/sec. But as dominant as parallel ATA is it suffers from three limitations that become more important as servers become faster and more robust.

Parallel ATA uses 5-volt signaling, which limits its use as companies try to reduce chip voltages and the use of large chip pads. It uses an 18-inch long, two-inch wide ribbon cable with 40 pins, which when squeezed into a server chassis severely restricts the available space for installing peripheral adapters and disk drives and restricts airflow, thus causing heat problems. Parallel ATA also has data protection issues that limit its reliability - it uses only a cyclic redundancy check and performs no checking of the ATA command data.

"Parallel ATA was never designed to be used in transaction-rich environments where you want all the error correction enabled that you can," says Dave Reinsel, research manager with IDC.

Instead, Reinsel says, it was used in environments where one drive was attached to a server and because of the applications run on it, was not as robust from an error correction point-of-view as SCSI was.

With SATA, the cables that attach drives to the server are thinner, longer and more flexible - they are 1 meter long, much thinner than the customary ribbon cable and have a six-pin connector - making it easier to install. SATA also supports hot-pluggable drives, letting IT managers replace failed or troublesome drives without taking the server down.