SAS STX A6-4

Serial Attached SCSI (SAS) is the next-generation replacement of SCSI Ultra320. SAS is a serialized protocol. The serial interface offers several benefits over the existing SCSI parallel bus; allowing for high availability, complex storage topologies, and a lower cost structure.

High Availability: As with SATA, Serial Attached SCSI is a high-speed, point-to-point technology initially designed to operate at speeds up to 6Gb/sec. System designers have found that point-to-point serial connections are inherently more reliable than shared bandwidth parallel connections. As a result, point-to-point serial connections have become the preferred method for implementing high-availability systems. SAS based disk drives are dual ported, taking advantage of this feature. This is a key requirement of high-availability SANs that call for redundant paths to all devices in the system.

Complex Storage Environments: SAS storage environments usually consist of a mixture of disk drives, host bus adapters and expanders. SAS allows for addressing of over 16,000 devices. SAS Expanders are routing devices that forward service requests between the source and destination devices. Expanders can be attached to other expanders, disk drives, and other hosts. An important characteristic of Expanders is their ability to aggregate bandwidth by combining multiple physical links into a "Wide" port. These wide ports can function as intelligent switches and can independently send commands across one physical path with data being returned over a different physical path. This increases the complexity of SAS test and debug because it requires users to monitor multiple links concurrently to record all DWORDs associated with a single SCSI transaction. The usage of expanders also allows for usage of a storage concept called Zoning. Zoning allows administrators to restrict access to devices by other devices. Applications of this include separating storage systems within a company by department.

Lower Cost Structure: Serial Attached SCSI also contains support for SATA drives in its storage environments. This allows support for both enterprise-class performance offered by SAS and low cost storage with SATA drives in the same system. Since the cost of the SAS infrastructure is expected to be comparable to SATA, it is likely that SAS will be the preferred interface. Since both SAS and SATA drives can be used in this environment, it will simplify and standardize the storage infrastructure, allowing for the ability to choose which drive will best fit individual storage needs.

SAS Test and Verification: LeCroy's protocol analysis tools are designed from the ground up to address these unique characteristics of SAS including wide-links and Serial ATA interoperability. Sierra’s analysis and design suites are developed specifically for use with the SAS and SATA protocols, and provide extensive protocol decoding, expert error analysis, and complete user support when decoding and viewing the recorded traffic. This extensive protocol support, combined with the different traffic views, advanced triggering, data filtering, traffic generation, and error injection capability, allows engineers to rapidly become familiar with SAS- and SATA-specific issues, and quickly understand new issues the first time they encounter them. Every engineer becomes a protocol expert with the support of Sierra’s detailed expert analysis.

The STX A6-4 supports up to four full-duplex links at data rates of 1.5 Gb/s, 3 Gb/s and 6 Gb/s. The STX A6-4 supports up to 8 GB of trace memory to allow long trace recordings to capture even intermittent errors. The STX A6-4 can also be cascaded with other STX A6-4 units, increasing the number of physical links that can be monitored (up to 32 physical links) through a single GUI.

The STX A6-4 features several customizable options for triggering and pre-filtering ensuring that relevant data is captured. Both the triggering and filtering capabilities can be accessed either through 'Easy' mode, which features simple 'click to add' functionality, or 'Advanced' mode which features a 24-level state sequencer with 1 IF and 3 ELSE-IF conditions per state. 'Advanced' mode also supports three independent timers and the ability to change pre-filters for each state. Trace/Buffer size as well as pre- and post-trigger capture is also user definable.

Captured traces can be displayed in a variety of ways to suit the analysis being performed. The Packet View decodes captured events and displays them with accurate time of occurrence and duration information. Link layer, transport layer, and application layer views are provided, using color to differentiate between each layer. Layers can be hidden, collapsed or expanded to vary the amount of data, from a meaningful summary to bit-level detail. The Spreadsheet View provides an organized chronological view of all bus events. Detailed information is provided on time stamps, duration, direction, source and destination addresses, command and/or picker contents. The Text and Column Views provide an intuitive understanding of frames, primitives, and other events, and includes at-a-glance addressing and summary indications of bus activity. The OOB Waveform View indicates OOB activities in waveform-like display. The captured OOB sequence is displayed in a graphical format, which represents the time relationships between the various OOB events.

Statistical summaries of the trace data are available at the click of a mouse button, and provide counts, timing, and performance information. Jumping from the statistical summaries to specific events is a simple mouse click, eliminating the need to search traces for events that may or may not be present. Comprehensive post-capture filters and search capabilities display relevant events with the detail necessary to isolate and solve protocol issues. When issues are found, bookmarks can be inserted in the trace to allow comments to be embedded for future reference.