STA

Author: Sam Barnett, Product Line Manager, Serial Attached SCSI and Serial ATA
Storage Products Division, Vitesse Semiconductor

Mention Serial Attached SCSI (SAS) technology to a gathering of IT professionals and the room is immediately charged with an air of excitement. Take the dialogue one step further and associate SAS with Fibre Channel front-ends/fabrics/switching or a Storage Area Network (SAN), and the mood turns somber – until economic reality sets in.

SAS technology offers a wealth of benefits to the enterprise server and enclosure customer (high reliability and performance, mixed enterprise/desktop drive support, improved economies of scale), but it was not developed with networking in mind. Even so, with modest extensions to the existing standard SAS could be positioned to dominate the changing storage network landscape.

This article explores SAS technology and its logical extrapolation as a viable protocol for the Storage Area Network (SAN) of tomorrow.

Author: Linus Wong, Director Strategic Marketing and Tom Treadway, CTO
Adaptec

For the past five years, your only choice for developing a high-availability, highly scalable and reliable storage subsystem has been to use a Fibre Channel (FC) storage area network (SAN)-based architecture. A number of key features have established FC as the platform of choice for the highest storage performance. It provides:

• Enterprise-class reliability
• 1 and 2Gb/s bandwidth, with 4Gb/s products entering the market now
• Support for multiple topologies
• Scalability up to hundreds of servers
• Flow control to eliminate congestion
• Mature set of storage network services

However, FC has not proven to be a universal solution because its price point and maintenance requirements have put its level of reliability out of reach of smaller organizations. For businesses that need low-end networked storage, Serial Attached SCSI (SAS) can provide similar reliability at a far more affordable price.

Although SAS was originally designed to replace the aging parallel SCSI interface as an inside-the-box connection in direct-attached storage (DAS) implementations, it actually has many of the qualities of a network fabric. For example, it scales easily without downtime by using expanders the way switches are employed in FC architecture. Like all multi-node environments, SAS allows multiple hosts to access various storage systems and also provides redundancy, offering multiple paths for a host to access its data.

Author: Martin Czekalski, Interface Architecture Initiatives Manager
Maxtor Corporation

Well, with a variation of that now-classic line, it all depends on what your definition of "fabric" is. If your definition includes a large computer room, campus infrastructure environments or generalized network capabilities, then the answer is "No." For example, if you have multiple computer rooms full of servers and storage area network (SAN)-attached storage with the need to connect a cross-campus environment, then either a Fibre Channel (FC) or IP-based SAN is going to be the obvious choice. These protocols and interconnects allow for a high degree of connectivity as well as long cabling distances. However, many applications that currently use SANs are much more bounded, and could easily be satisfied by using Serial Attached SCSI (SAS). Let's look at some usage models and see how SAS can provide many of the same features as a SAN in these bounded environments.

Author: Charlie Kraus, Director, HBA Business Unit
LSI Logic

Adoption of the next evolutionary step in SCSI technology, Serial Attached SCSI (SAS), is well underway, with announcements from major OEM storage vendors starting to appear. Initially the role of SAS was understood to be the next direct-attach technology for internal disk drives in servers, or for external drives in SAS JBODs. We will see just such applications of SAS technology in the beginning. But there are other aspects to SAS that will have wide-ranging implications and prove disruptive to current strategies for building storage systems.

Author: Samuel J. Barnett
Product Line Manager, Serial Attached SCSI Products
Vitesse

IT Insights
Mention Serial Attached SCSI (SAS) technology to a room full of IT professionals and the air is immediately charged with excitement. Take the dialogue one step further and associate SAS with Fibre Channel front-ends/fabrics/switching or a SAN and the mood turns noticeably somber.

While Serial Attached SCSI offers a wealth of benefits to the enterprise server and enclosure customer (high reliability and performance, mixed enterprise/desktop drive support, and improved economies of scale), the thought of yet another SAN technology initially concerns the majority of the end-customer community. Legacy deployments of 1, 2, and now 4Gbps Fibre Channel in conjunction with costly director-class switches make a wholesale technology shift difficult at best, while other promising technologies like iSCSI further divide the end-user community.