Serial ATA ensures data availability - Connectivity

Computer Technology Review, July, 2003 by Tracy Bowden, Jayme Bruno

Decisions about IT infrastructure continue to be influenced by a number of factors including rapidly changing technology, mandates to reduce or control costs, an enormous amount of data that needs to be stored, and new legislation regarding data access and retention. As a result, it's essential for companies to adopt and implement evolving solutions, such as Serialized AT Attachment (Serial ATA or SATA), that ensure data availability.

Seen as the replacement to the Parallel ATA (PATA) physical storage interface, SATA has a ten-year roadmap that will be able to keep up with the industry data transfer and storage needs. SATA technology delivers key scalability, price, performance, reliability, and cabling components.

SATA Advantages

As SATA is 100% software compatible with PATA, users wishing to take advantage of the technology do not need to worry about changing their current drivers and operating systems when upgrading. Options such as this, combined with the features and capabilities of SATA, have many industry watchers excited about the technology.

SATA brings a point-to-point interface that connects (by blind-mating and/or hot-plugging) storage devices such as hard disks, DVD, and CD-RW drives to the PC motherboard. Its point-to-point interface eliminates the need for master and slave accesses on the same cable. Blind-mating eases installation, allowing any cable from any port to connect to any disk drive. The advantage of hot-plugging allows for swapping out failed disk drives without powering down the system. SATA's direct connection also eliminates having to set termination and jumpers on the motherboard.

Another advantage that SATA presents is its thinner cables. With thinner cables than PATA, the airflow inside the enclosure is better and components are recognizable. The thinner, longer (up to 1m) cables allow for a more versatile enclosure chassis design (no master/slave) so, basically, more storage can be put into the same amount of physical space. Thinner cables ease the installation process, too--eliminating bending and weaving of the ATA ribbon cables and worries about damaging the cable pins.

SATA's support for lower voltages reduces pin counts and motherboard real estate requirements, providing the opportunity for a smaller form factor. Lower voltages also enable SATA to sustain the progression of smaller semiconductor manufacturing geometries. SATA cable connections have been reduced to 7 pins over the 40-pin PATA connection.

As SATA has evolved and continues to evolve, all major disk drive companies have adopted SATA technology which, in return, provides competitive pricing.

Currently, ATA has the majority of the low-end server and workstation market, while SCSI has the majority of the enterprise server market. The SATA roadmap suggests phases of implementation into the marketplace. With the release of the SATA I specification came the "Early Adopter Phase" where the availability of drives was limited and the majority of the customer base was from desktops, white-box workstations, and entry-level server markets. SATA II will be delivered in phases. Phase I, or the "Acceptance Phase" will support more deeply into the entry level server market as well as the NAS (Network Attached Storage) and rackmount markets. Phase II of SATA II, or the "Growth Phase," will continue to support server, NAS, and SAN environments.

A common practice of providing a secure environment for information is through the use of RAID (Redundant Array of Independent Disks) technology. Typically, RAID is used in large file servers such as transaction or application servers where data accessibility is critical, and fault tolerance is required. Today, RAID is also being used in desktop systems for CAD (computer-aided design), and multimedia editing and playback, where higher transfer rates are needed. When doing RAID implementations, SCSI technology has been the interconnect of choice for most IT organizations. Its high level of reliability, and performance has brought significant value by protecting mission critical data. Just as ATA has evolved with serial technology, so has SCSI (SAS). With SATA and SAS available, users are presented with flexibility in choosing the right option to meet their specific storage needs.

In storage environments requiring configuration simplicity and optimal cost capacity, combining SATA and RAID produces an enterprise data storage solution that brings storage technology advancement to the forefront. SATA RAID controllers can be either hardware-or software-based.

Building an enterprise SATA system can be fairly straightforward, with some companies offering bundled solutions. However, picking and choosing will work too. A cost-effective way to build a SATA system would be to utilize a half-size form factor controller with six ports. Plugging these controllers into six SATA drives will give terabytes of data storage capability, not to mention overall expeditious transfer speed.

Another aspect to look at is the type of enclosure to use. There are enclosures that can house the six drives, and that enclosure can fit into a typical 5.25 inch drive bay or a compact 2.5-inch form factor drive bay. So, looking at the big picture, it's multiplying the (drive bays) x (enclosure) x (SATA drives). This is a myriad of data storage capability at a relatively low cost.