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What is Serial-Attached SCSI? (From the SCSI Expert).

Serial-Attached SCSI was developed by leading enterprise and storage vendors and suppliers as a new storage interface to address the storage interconnect requirements of future enterprise environments. Serial-Attached SCSI combines the enterprise features of Parallel SCSI and Fibre Channel with the efficiencies of the Serial ATA interconnect. Serial-Attached SCSI leverages industry investments in the SCSI command set to provide enterprise-class reliability, performance, and manageability. Addition-ally, Serial-Attached SCSI leverages Serial ATA interconnect technology so that Serial-Attached SCSI can be compatible with lower-cost Serial ATA drives, simplify cable, connector and backplane designs, and to increase support and bandwidth scalability.

Serial-Attached SCSI is the logical evolution of Parallel SCSI that satisfies the data center requirement of scalability, performance, reliability, and manageability, while leveraging a common electrical and physical connection interface from Serial ATA. This provides users with unprecedented choices for server and storage subsystem deployment.

Why Is Serial-Attached SCSI Being Developed?

Serial-Attached SCSI is being developed to address anticipated I/O and direct attach storage requirements. It will provide universal interconnect with Serial ATA, while offering logical SCSI compatibility along with improvements in the reliability, performance and manageability of Parallel SCSI.

What Is the Difference Between Serial-Attached and Parallel SCSI?

Parallel SCSI is a proven enterprise-level technology for 110 and device requirements with a more than 20-year history of reliability, flexibility, and robustness. Parallel SCSI has limited device addressability as well as certain physical limits associated with the nature of its distributed transmission line architecture (performance and distance), plus large connectors that make it unsuitable for certain dense computing environments.

Serial-Attached SCSI will leverage the proven SCSI technologies that customers expect in data center environments, providing robust solutions and generational consistency. It will be based on a serial interface, allowing for increased device support and bandwidth scalability, reducing the overhead impact that challenges today's SCSI environments. It will provide easy solutions for systems through simplified cable routing. It will also utilize the Serial ATA development work on smaller cable connectors, providing customers a downstream compatibility with desktop class ATA technologies.

Finally, this simplified routing will enable a new generation of dense devices, such as small form factor hard drives, which will enable storage solutions to scale where traditional parallel SCSI cannot, due to cabling and voltage challenges.

When Will Serial Attached SCSI Solutions Be Available?

Development components such as HBAs, RAID controllers, enclosures, drives, and expanders will be available for evaluation in late 2003, with solutions in production beginning in 2004.

What Are Serial-Attached SCSI Expanders and What Function Do They Provide?

Expanders are simple virtual-circuit switches that provide scalability of basic Serial-Attached SCSI configurations. There are edge expanders typically enclosed in the drive enclosure, and fan-out expander devices for large configurations. Each expander can address 64 devices with a maximum cascade configuration of 4096 total devices in a Serial Attached SCSI domain. These expanders would be configured between the Serial Attached SCSI drives and the RAID controller.

Will the Industry Be Able to Sustain Four Different Interfaces With Serial ATA, Fibre Channel, Parallel SCSI, and Serial-Attached SCSI?

By leveraging leading OEM and IHV investment in current interface standards, the ability to produce and deliver Serial-Attached SCSI solutions will be very achievable. For customers, it also provides the best investment protection by combining the benefits and reliability of SCSI with the universal interconnect of desktop-class Serial ATA solutions.

Is Serial-Attached SCSI Development an Effort to Create an Interface or a New Device?

It is both an interface and for devices, which will be developed once the specification is final. When Serial-Attached SCSI is fully developed, standardized and available to the market, customers will be able to purchase end-to-end solutions addressing their enterprise requirements.

What Are the End User Benefits of Serial-Attached SCSI?

Key customer benefits of include enterprise class robustness, investment protection in compatible SCSI software, and the choice of direct-attach storage devices (Serial ATA or Serial-Attached SCSI). In addition, longer cabling distances, smaller form factors, and greater addressability will all lead to a new level of flexibility when deploying mainstream data center servers and subsystems. Since Serial-Attached SCSI is based on the foundation of the leading Parallel SCSI specification, reliability, and peace of mind will satisfy users' needs for continuity in the data center.

Is Serial-Attached SCSI Complementary to or Competitive With Parallel SCSI?

Serial-Attached SCSI is complementary to Parallel SCSI. Parallel SCSI is a proven enterprise-class technology for I/O and device requirements. Serial-Attached SCSI will leverage the proven SCSI technologies that customers expect in data center environments, providing robust solutions and generational consistency. It will be based on a serial interface, allowing for an increased number of devices and future bandwidth scalability. Simplified cable routing will provide easy solutions for systems. It will also utilize the Serial ATA development work on smaller cable connectors, providing customers a downstream compatibility with desktop class Serial ATA. Finally, this routing will enable a new generation of dense devices, such as small form factor hard drives, enabling storage solutions to scale externally.

Is Serial-Attached SCSI Complementary to or Competitive With Fibre Channel?

Initial implementations of Serial Attached SCSI will have support for greater than 128 addresses and provide dual-ported device support. Fibre Channel will continue to evolve as the interconnect and device solution for large enterprise storage configurations, offering up to 16 million addresses, and longer cabling distances of 10 kilometers. Serial-Attached SCSI is a more bounded configuration that will initially be targeted at direct-attach storage environments, server, device attachment to RAID controllers, and bounded out-of-box connection schemes.

Is Serial-Attached SCSI Complementary to or Competitive With Serial ATA?

Serial-Attached SCSI complements Serial ATA by adding device addressing (scalability), and offers higher reliability, manageability, and data availability services, along with logical SCSI compatibility. It will continue to enhance these metrics as the specification evolves, including increased device support and better cabling distances. Serial ATA is the best choice for desktop, servers and networked storage where price is the primary selection factor. Most importantly, these are complementary technologies based on a universal interconnect, where Serial-Attached SCSI customers can choose to deploy cost-effective Serial ATA in a Serial-Attached SCSI environment. In summary, customers requiring the best price advantage for server and storage deployments should choose Serial ATA and customers requiring maximum performance, reliability and software consistency should select Serial-Attached SCSI.

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Author:Dubinko, Micah
Publication:Computer Technology Review
Geographic Code:1USA
Date:Nov 1, 2002
Words:1046
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