Agilent Measurement Journal - Issue 4 - 2008 - (Page 36)

Addressing the scalability challenge When using hand-built test systems based on real servers and storage devices, scaling up to validate a conﬁguration that has several hundred ports might require dozens of large racks ﬁlled with equipment. It also would require a lot time to maintain all of the equipment and ensure proper operation, as well as a lot of electricity to power everything. Dedicated SAN-test platforms replace those racks of real hardware — and reduce the physical footprint — by emulating the behavior of servers and storage devices (Figure 3). Each port of the test device can be conﬁgured to mimic multiple types of active devices. As one example, each physical port of the Agilent 173x Fibre Channel SAN test system can mimic 126 devices. Creating a test environment of 1000 devices requires only eight tester ports, which would occupy just 2U of vertical rack space. In terms of control and coordination, a dedicated test system offers additional advantages. To control real devices, the test engineer typically needs to log in to each device individually (or can write scripts to automate the process). In contrast, a dedicated test system typically includes a GUI that provides a single point of control over hundreds or thousands of emulated devices. Figure 1. The ability to view real-time statistics in tabular and chart formats enables rapid understanding of device behavior. In most cases, test systems easily can create operating scenarios that are expected by the device (positive testing). Because the SAN tester has been purpose designed, however, it also can create unexpected operating scenarios (negative testing). These negative tests are essential to understanding the behavior of a device under stressful or unexpected conditions. For example, a switch in a network might be connected to a faulty server that is rebooting every few minutes. A test engineer would want to understand how the switch behaves in such unexpected conditions. By testing for this scenario, the engineer can determine if the switch might cause a catastrophic failure across an entire network when deployed in the ﬁeld. This is one of several types of negative testing the SAN tester is designed to address. Protocol analyzers are another important tool in SAN testing. Detecting failure symptoms and retrieving the root cause of functional problems becomes more challenging as the number of ports in a SAN increases. Having access to trafﬁc history before a failure is essential; a protocol analyzer can provide better visibility into the problem and a clear picture of ongoing communication and protocol exchanges. The protocol analyzer should provide tools and features that enable clear visualization of the system being debugged, and different analyzers use different approaches. One example is the Agilent Fibre Channel protocol analyzer, which includes advanced graphical user interface (GUI) capabilities that highlight the information ﬂows moving through a multi-node system (Figure 2). To help the user quickly isolate problems, each type of frame is color coded, eliminating the need to stop and read the text in each one. Addressing the cost challenge In a recent survey conducted by Agilent, a majority of respondents identiﬁed “budget” as the most important factor when assessing testing and test needs. This was not a surprise: while SANs — and their test needs — are growing, budgets are being held constant. For test teams and data-center staff, this means ﬁnding creative ways to do more with less. One solution is dedicated test systems. On a per-port basis, test tools might be more expensive than real devices; however, because the test device can emulate hundreds of devices on a single physical port, the total cost of test will be lower. Multifunction test equipment provides another way to reduce the cost of testing. Historically, SAN testers and protocol analyzers have been separate devices manufactured by different vendors. As a result, organizations bought at least two instruments and two applications to cover their test and debug needs. This model was costly because it needed to account for peak usage of individual instruments and the ports 36 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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