Serial ATA Basics

Introduction
The emerging Serial ATA (SATA) interface technology is expected to eventually replace the Parallel ATA (PATA) technology that currently occupies 80% of the total hard disk drive market. SATA offers the promise of much better system performance than found with PATA systems, yet at a fraction of the cost of traditional storage technologies such as SCSI or Fibre Channel. Primary industry supporters of this technology include Intel, Dell, IBM, Maxtor, and Seagate.

Background
ATA (Advanced Technology Attachment), also known as IDE (Integrated Drive Electronics), drive technology has been around since the mid 1980s. Until recently "ATA" has been simply identified a 16-bit parallel connection, initially supporting a 3.3MB/s throughput. However, PATA has gradually evolved to now support up to 133MB/sec.

As data rates have increased, signal reflection and signal skew limitations have made it difficult for the 40-conductor PATA interface cable to successfully reach its maximum length of 18 inches; PATA is obviously reaching its maximum performance capacity. To specifically surpass these technical limitations and address the ever-increasing desire for higher speed and larger capacity drives, SATA was created.

SATA Benefits
The benefits of systems implementing the SATA interface technology can be best described by comparisons to PATA systems.

Cabling/Connection: SATA uses longer, thinner more-flexible cables than traditional PATA cables, which are bulky, fragile and short. SATA also uses a compact 7-pin data connector, as opposed to the 40-pin connector used for PATA interfaces. SATA cables are much simpler than PATA cables to route and install, and their compact nature leaves more available component space on motherboards and disk drives. These features support hardware design flexibility and ultimately simplify configuration of storage devices in a SATA-based system.

Airflow Management: Bulky cables connected to disk drives are not only more difficult to set up, but they also block airflow and induce heat. These factors affect the overall performance and stability of the hardware. The narrow 7-pin SATA cable/connector improves thermal management without blocking airflow (unlike the 2" ribbon cable required with PATA).

Performance
Bandwidth: SATA drives use a point-to-point connection to the system. By using point-to-point topology, as opposed to a bus-based architecture found predominantly in PATA or SCSI technologies, SATA can deliver full bandwidth to each connected drive, which improves overall performance.

Transfer Rates: The SATA road map consists of three generations of increased data transfer rates: 150, 300 and 600MB/sec device burst rates.

Encoding: The SATA interface technology uses 8B/10B encoding, a method for encoding 8-bit data bytes to 10-bit transmission characters. Using serial technology with 8/10 encoding improves overall transmission and completely bypasses parallel transmission problems. This high-data-integrity scheme provides timing and integrity checking provisions required by high-speed transmissions.

CPU Usage: SATA devices are not dependent on host controller for DMA support. This means that CPU usage can be lowered to attain increased performance, and it allows SATA interfaces to be ideal for server applications.

Voltage Requirements: SATA uses low-voltage differential (LVD) signaling, which is associated with low power consumption and cool temperatures. 5-volt signal requirements associated with PATA are only 0.25 volts for SATA, enabling lower power handling on the drive and reducing the required size of switch controllers.

Compatibility: The SATA standard is also backward compatible, making it simpler to convert between Serial to Parallel formats and also speeding up the industry adoption rate of SATA.

SATA for RAID
The SATA interface technology presents the possibility of supporting large storage arrays at prices and with performance levels ideally suited for near-line storage of business information, such as archived emails, corporate reference materials and other information that does not require frequent access. But such systems have sufficient differences from arrays based on SCSI and Fibre Channel technologies, in that they present new design challenges in the areas of signal integrity, enclosure management, hot plugging and power distribution.

The best way to assure that an SATA system will manage these new challenges and ultimately meet the performance and operational intentions of a particular application, is for users to communicate and coordinate product features and roadmaps with their drive and enclosure manufacturers and suppliers.

StorCase's SATA RAID
The StorCase® InfoStation® 12-Bay backplane rack mount enclosure is available in models which include either a SCSI-to-SATA or Fibre-to-SATA RAID controller, providing a unique feature that allows support of both PATA and SATA drives. The included high-performance RAID controller supports RAID levels 0,1, 0+1, 3 and 5. These models also provide an open 5.25 inch peripheral bay that can accommodate a tape drive; making this an ideal product for disk back-up.

The SCSI-to-SATA InfoStation supports dual SCSI Ultra160 SCSI channels, connecting drives through a proprietary connection for ultimate reliability. A maximum of four arrays can be created, each containing up to eight partitions. Performance tests with this enclosure have been reported to show an 81% improvement over PCI-based Serial ATA RAID arrays.

The Fibre-to-SATA InfoStation enclosure is perfect for applications such as SAN, clustering, streaming video and heterogeneous storage, which require high throughput and continuous uptime with a 2Gps host interface. Due to its throughput advantage over SCSI, and also its ability to provide the bandwidth required for streaming video, the Video Editing Industry has been using Fibre implementations for Direct Attached Storage (DAS) applications. Configured with (2) separate 2Gbps loops connected to different hosts, the Fibre-to-SATA InfoStation is an ideal DAS product. As networked storage applications become more frequent, the InfoStation has an ideal place as networking storage product, capable of unsurpassed performance when configured for dual 2Gbps loops interfacing to an FC switch.

The environmental status of system parameters can be monitored by the InfoStation's free browser-based utility, InfoMon®. The InfoStation can be configured to send email, fax, or page alert messages to system administrators via modem and can also be rebooted remotely.

Each InfoStation is designed for multiple storage environments and offers top performance and protection for today's high-capacity drives. As with all StorCase enclosures, the InfoStation is designed and constructed to provide excellent thermal and Rotational Vibration management to assure maximum drive performance and longevity. This emphasis on data security and system performance, combined with the relatively cost-effective nature of SATA drives, allows this enclosure to satisfy both the technical requirements and the budget constraints of today's IT organizations. The cost of SATA drives is still about 15% more than that for PATA drives, but SATA is expected to be very cost competitive with PATA in the near future.

StorCase is a member of the Serial ATA Working Group. The Serial ATA Working group was organized by the technology leaders in this field to help standardize the technology, to ensure interoperability and to offer technical resources http://serialata.org.