Verifying System Reliability for SAS Integrators

Author: Mike Micheletti, Product Manager
LeCroy Corporation

Now that component vendors Serial Attached SCSI (SAS) are shipping in volume, storage integrators are rolling up their sleeves to begin evaluating this powerful new storage interface. Anxious to harness superior performance, these SAS developers are testing hosts, devices and storage subsystems for compatibility and reliability. Early adopters are impressed to see their legacy SCSI applications running on top of SAS storage volumes without modification. But is SAS robust enough to replace parallel SCSI in mission critical applications?

LeCroy’s InFusion is a new test tool that allows users to verify fault handling at the system level. Unique in the marketplace, InFusion is designed to sit unobtrusively in the data path on a live system and programmatically alter or corrupt traffic. It can intelligently change the traffic to help developers evaluate the resiliency of individual SAS components. But what makes SAS InFusion ideally suited for testing a new storage architecture is its ability to verify error recovery at the system level. Because InFusion works with real traffic and actual workloads, it allows vendors to verify recovery in a “real world” operating environment.

Unlike traffic generators, InFusion is easy to use. A menu-driven interface allows users to create custom test scenarios in minutes. Test scenarios can be set to periodically insert frame errors like invalid cyclic redundancy checks (CRCs) or running disparity errors. But it can also be used to change any field, within any frame, as the data moves across the bus. Any primitive or data pattern can be intercepted and changed to a different pattern. This allows for an unprecedented corner case and protocol-level error injection for SAS and SATA traffic.

Once the InFusion system has been added to a SAS or SATA link, it automatically passes the boot-up sequence and preserves protocol handshaking between devices. It silently monitors the line while transmitting a faithful copy of the original data stream. The system will wait for a specific time interval or count a particular event that you designate before it begins modifying frames or injecting errors. InFusion can be configured to send a single error, multiple errors, or random errors.

When changing fields within a frame, the InFusion traffic modifier will preserve the outbound frame structure, including recalculating the CRC if needed. The response transmitted from the device under test will pass through the InFusion system, without modification. This enables true end-to-end system testing. Multiple InFusion systems can be combined to inject errors simultaneously on multiple physical links.

The InFusion system is perfect for developers looking for an easier way to verify the resiliency of storage subsystems using SAS technology. It allows users to verify that SAS is up to the task of replacing SCSI and Fibre Channel in mission-critical applications.

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