Serial ATA disk drives have a transfer rate of up to 150MB/sec and a cost that places them above parallel ATA - what are known as IDE drives - but below SCSI drives. SCSI drives are used in workstations and servers where fast access to data is needed. Parallel ATA drives rule on the desktop where a price/performance balance has to be struck. These drives are also beginning to be used in servers. There, in an array form and with RAID technology to guard against their relative unreliability, they provide disk storage for backup of the main, SCSI, disks and storage of fixed content - data that will be accessed less often than primary data.

EMC's Centera file store is a prime example of a fixed content ATA storage array, as are Network Appliance's NearStore and StorageTek's EchoView.

SATA SME and throttling
Where will SATA drives find their niche? The consensus view is that small and medium businesses will be the prime market, with high-end PCs and workstations also using the technology. However, PC bus limitations will throttle SATA drives until a PCI bus replacement arrives.

Western Digital says its new SATA-equipped hard drives feature capacities as large as 250 GB, together with an 8MB buffer and three-year warranty, to fill demand in market segments such as the high-end PC, workstation and entry-level servers.

"Explosive data growth among small and mid-size businesses is increasing demand for storage solutions that deliver cost-effective server connectivity, enterprise-level data protection and greater throughput," said Roger Cox, Research Vice President, Server Storage and RAID Worldwide, for Gartner Dataquest. "Serial ATA combines all three to improve application performance and bring the cost of data reliability to a point where virtually all data can be stored on redundant systems."

Dave Reinsel, an IDC analyst, offers this view; "Currently, SATA drives are finding homes in the high end of the PC and workstation markets, as well as in the entry-level server and storage subsystem market. (We) anticipate the adoption of SATA hard drives in the enterprise market will continue steadily because the technology offers system-design flexibility advantages over Parallel ATA, and cost and capacity advantages compared with enterprise-class hard drives."

IDC reckons SATA will replace PATA in most new PCs within the next two years. It thinks PATA hard drives currently represent about 10 percent of the overall enterprise market segment and SATA, replacing PATA, will grow to nearly 40 percent of the enterprise storage market in 2006. RAID controllers will help this.

SATA RAID arrays
SATA RAID product releases are coming thick and fast.

• Adaptec is with Western Digital in thinking that SATA opens up an SME niche between more expensive SCSI and cheaper desktop ATA drives. It is bringing out SATA RAID controllers and its Storage Solutions Group VP for Business and Marketing, Steve Cochran, says, "Adaptec is combining its enterprise-class RAID capabilities with Serial ATA's fast data access and low price-per-gigabyte to help small and midsize businesses better move, manage and protect information."
• Highpoint has also released its 1540 SATA RAID controller; one of the least expensive to be found anywhere that supports RAID 5.
• A line of Serial ATA MegaRAID products from LSI Logic is now shipping and includes battery backup for enterprise-class fault tolerance and data protection.
• StorCase Technology's (a Kingston Technology Company) InfoStation Serial ATA (SATA) RAID enclosure, with up to 3TB capacity, will launch in August 2003.
SATA hot pluggability, supported by Windows in a 2004 release, will help the entry of SATA RAID into the SME market.

Releasing the throttle
Serial ATA will get faster as the technology is developed. The transfer rate will double to 300MB/sec in 2004 and then again to 600MB/sec in the 2005/6 period. However getting data off the drive is one thing. Getting it across the PCU bus at a sustained high speed is another. Current PCI bus attributes limit SATA disk speeds to parallel ATA levels. But the coming PCI Express, another serial technology, will unshackle the SATA drives. Intel and many PC vendors are pushing this technology hard.

Small business SATA RAID arrays are coming. We can expect the fixed content arrays from EMC, Network Appliance and StorageTek to embrace SATA next year. It will be designed into new PCs and x86 servers later this year because of the cabling and cooling advantages it offers. From next year, when the first PCI Express systems appear, we should see a significant increase in data access rates with desktops, workstations, small servers and fixed content arrays all faster than ever.