Serial ATA ensures data availability.

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.

With the majority of half-size-form factor SATA controllers comes the ability to choose a number of RAID levels (0, 1, 5, 10, or 50). Whether it's 100% data redundancy with RAID-l, or very high data throughput and no fault tolerance with RAID-0, or a combination of both, it's pretty much a win-win storage solution.

Another interesting aspect worth mentioning is a SATA controller with a BBU (battery backup unit) on board. The BBU provides a battery backup for data currently stored in the on-board cache memory during intermittent power loss to the controller. In the event of a power failure, the BBU can hold data in the cache for a certain amount of time. Once power is restored to the controller, the data can be saved to disk. This is a good enhancement for data protection, especially in RAID-5 types of applications.

SATA Limitations

It is often asked if the SATA Storage Solution really has transfer rate of 150 MB/sec. The answer is that the capability is there; but the reality is that it cannot deliver yet. However when using a setup like the solution previously discussed in this article, the transfer rate is multiplied; thus, it does achieve an overall higher transfer rate. Furthermore, drive manufacturers have not yet matched the enterprise-level features (speed, reliability, mechanicals) with the low price typical of the IDE/SATA market (e.g., SATA drive access time is >2X than SCSI).

Although SATA is software-compatible with PATA, it lacks seamless backward compatibility with existing ATA devices. When migrating from a PATA to SATA system, hardware changes are required to the hard drive, cable and connector interface.

Another limitation is that the current SATA Storage Solution doesn't fit all storage applications, the SATA specification did not implement some of the same features as the advanced SCSI protocol, including detecting errors. For example, if a fan fails and the temperature exceeds the disk drive capability of operating under that temperature, there is no audio or visual indication. Current SATA devices lack the intelligence to perform command queuing as well as SCSI does (which can queue up to 256 commands per logical unit).

The Future

SATA II will improve SATA I features and performance while retaining its compatibility and cost benefits. Phase I of SATA II will support backplane interconnect for use with multiple disk hot-swapping, Native Command Queuing, out-of-order execution/delivery, and data in both cable and backplane attached applications. This phase will also address Enclosure Management (fan control, drive lights, temperature control, new device notification, etc.) in the arena of entry-level servers, NAS, and rackmount markets. In order to enable full use of the host bandwidth, the use of port multipliers will increase support for multiple device connections (up to 15) when enclosures do not have sufficient SATA connections fur all of the enclosure drives.

In Phase II of SATA II, the migration from PATA will be complete and the Growth Phase will continue to improve transfer rates to a higher speed of 3.0 gigabits per second (300 MB/sec). Users will also be able to realize 3.0Gb/sec command queuing, and Active-Active Topology in the server, NAS, and SAN environments.

SATA II compliance (including enclosure management) and PCI-X are the trends for next generation SATA RAID controllers. These are key features that will enable SATA RAID to directly compete with the capabilities of SCSI RAID and extend the reach of SATA RAID beyond that of the IDE RAID domain. Other features will include Error Correcting Code for generating redundant information that can be used to detect and correct errors in stored transmitted data.

Although IT budgets are reducing in this slow economy, realizing high uptime and effective failover data protection at minimal cost does not have to pose a problem. Implementing SATA, and knowing that its future roadmap can support business and market climates, will be essential for success.

www.Isilogic.com

Tracy Bowden is product marketing manager and Jayme Bruno is marketing technical writer at LSI Logic RAID Storage Adapters Division (Milpitas, CA)

Comparison          PATA             SATA         SATA Advantage

Transfer Rate   3MB/s-133MB/s      150MB/s-       6X performance;
                  (Maxtor)         -600MB/s       Productivity

                                                  Less power
Voltage            5 Volt           250 mV        consumption, less
                                                  heat, ideal for
                                                  mobile use

Cable &          18 in., 80-      <1m, Thin &     Easier cable routing;
Connector        Conductor,       Flexible 4      Improved ventilation
                40-pin Flat       signal pins
                   Ribbon

Hot Plug         No standard     Supported w/     Up-time; data
                   Defined         Standard       availability,
                                    Defined       business continuity
                                                  Eliminates master/
                                                  slave

Connectivity       Shared        Point-to-Point   confusion; improved
                (Master/Slave)                    performance

Table 1- Comparing Serial ATA (SATA) to Parallel ATA (PATA)

SATA Ports        RAID Levels                       Target Markets

2 to 4            RAID 0, 1, 10 (for 4 port only)   -Desktop
                                                    -Workstation
                                                    -Low-end Server

4                 RAID 0, 1, 5, 10                  -Server
                                                    -NAS appliance

6, 8, 12 and up   RAID 0, 1, 5, 10, 50              -Server
                                                    -NAS appliance
                                                    -Rackmount Storage

Table 2--Which SATA/RAID controllers are used for which storage
environments? Here's what is available today.