STA

Author: David Allen, Director of Strategic Marketing, Storage Products Division
Vitesse Semiconductor

Serial Attached SCSI (SAS) expander architectures provide flexible, cost-effective connections for internal and external storage subsystems in the mid-range and enterprise server markets. In this article we address SAS expanded architectures applicable to both server and storage enclosure applications.

Expander Types and Features

SAS Edge Expanders and Fan-out Expanders provide switching for connecting multiple targets to a host connection. Edge expanders support up to 128 SAS PHYs. Similarly, “Edge Expander Device Sets” can be constructed from multiple edge expanders. Direct connections, subtractive connections, and limited table routing enable communication between individual expanders (see Figure 1). Because they employ limited table routing, edge expanders are targeted at low-cost designs with limited storage scalability requirements.

Author: Mike Micheletti
Computer Access Technology Corp. (CATC)

Scalability can be defined as "the ease with which a solution or component can be modified to fit the problem as the size of the problem increases". Scalability in the storage domain allows IT managers to respond to changing storage requirements within the enterprise, and is a stated design goal of Serial Attached SCSI (SAS).

The SAS protocol delivers scalability via Expanders, integrated circuits (IC) that function as switch components and route frames between initiators and end-points. By providing multiple point-to-point drive connections in a single IC, expanders allow aggregation of bandwidth between Initiator and multiple SAS disk drives. Expanders also enable an architecture that accommodates dynamic discovery and configuration as new components are added to the system.

Authors: Franco Castaldini and Kent Bransford
Seagate Technology

The arrival of Serial Attached SCSI (SAS) marks a new era in storage scalability, wherein both the type and quantity of drives can easily be optimized. SAS compatibility with Serial ATA (SATA) enables seamless deployment of desktop-class SATA drives and enterprise-class SAS drives in the same SAS domain, giving IT managers unprecedented flexibility to specify the most appropriate drive for both online (transactional, high availability) and near-line (archival, low availability) duties. Moreover, employing a common SAS infrastructure for both types of drives minimizes hardware redundancy, further enhancing efficiency.

Author: Ahmad Zamer
Intel Corporation

On a recent trip to the North East, I had the opportunity to visit the data centers of two corporate customers. The first was an Internet Service Provider (ISP), the second, a mid-size brokerage firm. Both organizations, despite their different businesses, spoke of similar challenges their Information Technology (IT) staffs face. They also spoke of similar needs they wanted to be able to meet using new technologies.

Real-World Data Center
The ISP's manager of data center operations spoke in terms that may not be unfamiliar to technical people who work on industry standard and storage product design. He talked about his needs and challenges in terms of how they relate to floor tiles. He measured the value and utility of every storage and server solution in terms of how much precious real estate they would occupy in his data center. Following a three-hour tour and lecture from the data center director, one finds it hard not to measure everything using the "tile factor."

From the ISP's perspective, the major challenges were the limited power, per tile, they can bring to the data center, and the ever-rising costs of cooling per tile. These are simple metrics that have serious implications for all new computing technologies, especially storage technologies. Pointing to huge boxes scattered across the data center, our guide shouted, "Do you see these huge boxes? These are my storage boxes and I don't seem to ever have enough." So, how can one keep adding big storage boxes to the enterprise infrastructure without negatively impacting the tile factor?