STA

By Paul Vogt, Director of Product Marketing,
Adaptec

The flexibility of Serial Attached SCSI (SAS) allows it to be used as a universal connectivity standard for a wide range of business needs. In addition to its role as a replacement for parallel SCSI, SAS now offers the ability to reduce the cost of servers and storage networks, to create tiered solutions that weren't possible before, and to provide investment protection for SATA installations. While SAS performance and scalability generate a majority of the media attention, it could be the flexibility that SAS brings to storage subsystems that creates the most value for your business.

SAS as a parallel SCSI replacement
SAS maintains support for the proven SCSI command set while offering much better performance, scalability, and availability. Stability and reliability have made parallel SCSI the standard in storage connectivity for twenty five years. SAS offers compatibility with this command set while overcoming the physical limitations of parallel SCSI. Now with SAS, it is possible to take advantage of dual-port drives, redundant connections, failover support and scalability up to 128 attached devices and over 16,000 addressable devices. Performance at 3Gb/s per port can be aggregated into wide-port connection bandwidth.

Author: Brad Corrion, Product Marketing Engineer
Intel Corporation

The evolution and innovation of a new technology generally is paced by the demands of its user base. New technologies can grow and adapt quickly, rapidly responding to the needs of a small user base. Ironically, when the technology becomes popular and entrenched, the innovations focus on extending the shelf life of the current technology to minimize user disruption. For example, parallel shared bus architectures such as PCI were made wider and clocked faster in order to move more data more quickly, but without significantly altering their underlying architecture to support backward compatibility.

When simple extensions no longer address fundamental technological challenges, radical reinvention occurs. The best bits are retained and the rest is reconsidered. Again, consider the parallel shared PCI bus that is quickly being replaced with the serial, point-to-point PCI Express bus. They share many conventions and compatibilities, but the technologies are fundamentally different.

Similarly, the storage industry is witnessing SCSI's big leap to Serial Attached SCSI, or SAS. Like PCI Express, SAS drastically reduces the scalability and design challenges of parallel SCSI while also bringing new capabilities which parallel SCSI could not offer. Timed to leverage SAS adoption momentum, the recently launched Intel IOP34x Storage Processor Family integrates SAS/SATA controllers into the sixth generation of Intel's I/O processor line to provide end-product ease of use, data protection, and the flexibility of multi-protocol storage technologies.

Author: Paul Griffith
Adaptec

Introduction
Today, most data centers use parallel storage technology like SCSI, but as requirements for increased performance, higher scalability and improved reliability grow, IT managers are looking to new serial technologies such as Serial Attached SCSI. IT managers needing a simple, cost-effective way to migrate from parallel-technology to serial-based systems with minimal disruption to business operations will find direct-attach storage (DAS) spillover, adaptive storage migration, and DAS evacuation powerful tools for enabling this transition.

Seagate Technology recently met with storage architect from a Fortune 500 Company located in St. Paul, Minnesota to get his insights on the issues surrounding migration from parallel SCSI to Serial Attached SCSI (SAS). In the following interview, our storage architect shares his views on why moving to SAS will ensure the flexibility needed to meet the storage challenges of today and tomorrow.

Author: Marty Czekalski
Maxtor Corporation

Years ago, nearly all interfaces were serial. Communications, printers, and disks all used serial interfaces. Those were the days of discrete components, and reducing the component count was an important factor in keeping costs under control. As the level of integration increased, it became possible to put multiple drivers on the same piece of silicon as the logic. This made parallel interfaces both high-performance and cost-effective. As a result, parallel interfaces became the rule and serial interfaces the exception, except in long-distance communications, where the cost of the high-speed transmitter/receiver technology was offset by the savings in wire (or fibre) costs.

Interestingly, as technology has moved forward, the same advances in integration that caused parallel interfaces to gain favor are now working against them. The I/O cells are not scaling at the same rate as internal logic, and it is now easier and less costly to add sophisticated signal processing at lower cost than adding additional I/O cells needed by parallel interfaces. The result is that these high-performance serial interfaces are becoming cost effective at shorter and shorter transmission distances as the levels of integration increase. We now find ourselves switching back to serial interfaces such as USB for printers and PCI Express for PCI replacement. The next step will see this same migration in the interfaces we use to connect disk drives. The evolution of ATA and SCSI will move these interfaces to Serial ATA and Serial Attached SCSI. This article will explore some of the details driving this transition as well as the advantages of these serial topologies.