Make way for serial attached storage

LONG BEACH, Calif.'The storage industry's next big wave of change will be the growing use of serial attached storage devices.

'There is paradigm shift going on now. We're going from parallel technologies to a serial environment,' said David Deming, president of technology training company Solution Technology of Ben Lomond, Calif. Deming spoke at the Storage World Conference being held this week.

'What you will see is serial [advanced technology attachment devices] becoming the main interface in probably every computer environment you encounter today,' Deming said.

The change involves the type of internal cables and controllers connecting hard drives and other peripheral devices to computers and storage arrays.

Most of today's desktop computers use some form of parallel advanced technology attachment, or Parallel ATA, to interface with their drives. Parallel ATA is designated as 'parallel' because the cables have 16 side-by-side wires, through which the data is sent. Traditional storage arrays use a similar parallel approach, called the small computer system interface. SCSI differs from Parallel ATA in that it offers the ability to attach more devices to a single bus.

Although long used by the computer industry, 'parallel technology is basically at an end,' said Martin Czekalski, vice president of the SCSI Trade Association. Serial technology sends data along only a single wire, though it can offer higher throughput than parallel approaches, thanks to advances in processors. A serial connection can offer throughput speeds of 1.5 Gbps per second, or about 150 MB per second. The fastest parallel connections offer a maximum of 133 MB per second.

Processor makers have offered Serial ATA, or SATA, chip sets for several years, and more motherboard manufacturers will start selling more SATA-only boards in the upcoming year, according to Czekalski. 'We will also start to see serial attached SCSI, known as SAS, offerings beginning in early 2006,' he said.

Serial attached storage 'fixes a lot of roadblocks,' inherent in both Parallel ATA and SCSI, Deming said. In addition to speed gains, these new technologies can also support more drives than their parallel brethren.

Parallel ATA can support only two drives per cable. SATA puts only one drive on each cable, though up to 15 drives can be connected by using a small device known as a port expander. In a similar fashion, SAS can support a basic configuration of up to 128 drives, and more drives can be added with successive port expanders, Czekalski said. In contrast, standard SCSI has a limit of 15 drives per cable.

SAS and SATA also simplify configuration. With SAS, administrators don't have to give drives assignment numbers or place a terminator at the end of each cable, Deming said. With SATA disks, administrators do not need to hand-set jumpers to designate the master-slave status of the drive, a necessary action with Parallel ATA disks.

'SATA and SAS are going to happen. Whether you like or not, they're coming out,' Deming concluded.

About the Author

Joab Jackson is the senior technology editor for Government Computer News.

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