The Anti-stress Advantages of SAS

Author: James Pascoe
Hitachi GST

Hitachi recently interviewed David Steele, Director of Product Planning and Management for Storage Standard Products in the Storage Components Division of LSI Logic Corporation. LSI Logic is a leading designer and manufacturer of storage, communications and consumer semiconductors for applications that access, interconnect and store data, voice and video.

Steele has more than 20 years of experience in the semiconductor industry and is currently responsible for defining roadmaps for LSI Logic’s storage standard product IC’s, including SCSI, SAS and Fibre Channel solutions. Hitachi asked Steele what IT departments should consider as they prepare to deploy SAS-based storage, including issues such as ease-of-use and management, interface performance, investment protection, etc.

Q: What are the key benefits of a dual-ported interface from the IT perspective?

A: The most important thing is that it enables a level of reliability in entry-level direct-attached storage (DAS) architectures that has previously been the exclusive domain of Fibre Channel SAN architectures. Dual ported Serial Attached SCSI (SAS) disk drives will enable full failover capability in a system that is closer to an entry-level configuration.

Q: How much will performance of the interface increase and how soon will the increase be available?

A.The industry has been accustomed to performance increases in parallel SCSI about every two to three years. I think it is reasonable to expect second-generation SAS (6Gb/s) to become available by 2007.

Q: What are some of the key challenges to users that will benefit storage cost and functionality?

A: The point-to-point architecture of the SAS interface will be new for some users that are accustomed to parallel SCSI. The good news is that the cabling is simpler and from a software standpoint, there are no major differences between SAS and SCSI. Current Fibre Channel users will find SAS extremely easy to work with.

Q: How many ports will be on a SAS controller?

A: Four ports is an incremental building block that is driven by the x4 external connector. We expect that 4- and 8-port solutions will be most common in the near-term. The intended application is what will drive the purchase decision between the two. For example, 4-port controllers will be used in server blades, some rack mounted servers and in non-server applications such as workstations. Users will likely want additional flexibility for their internal and external storage arrays and will opt for an 8-port controller.

Q: In terms of optimal system design and capacity what role will expanders play?

A: Expanders are primarily playing a role in external storage rather than in servers. These will likely be rack-mounted systems with 3.5-inch and 2.5-inch “small form factor” drives that use expanders to support anywhere from 12 to 30 or more drives. Expanders will also be used to set-up small storage clusters with full failover capability.

Q: How will customers be able to protect their existing SCSI investment after moving to SAS?
A: SAS will eventually replace parallel SCSI but during the interim users will be able to purchase adapter boards to support legacy Ultra320 SCSI, tape systems, etc.

Q: How much interest are you seeing in SAS among your customers?

A: The interest level in SAS has been tremendous. In fact, I cannot name a single top-tier enterprise server supplier that is not fully supportive of SAS. Suppliers of external Fibre Channel storage may take a “wait and see” approach and first let SAS prove itself, demonstrate cost benefits, etc. Once 6Gb/s SAS hits the market they will be forced to examine whether it is a viable alternative to 8Gb/s Fibre Channel.

Q: When do you expect to see widespread deployment of SAS systems on the market?

A: SAS controllers should be available by the end of 2004 and OEMs are expected to begin deploying systems in early 2005.

Storage systems based on the Serial Attached SCSI (SAS) architecture are anticipated to provide numerous benefits to IT department managers. Some thoughtful decision-making and consideration of all relevant factors can help IT managers draw the greatest value from this new technology.

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