The LeCroy SATATracker Command Analyzer monitors command execution and completion in SATA storage subsystems. By focusing its analysis on native command queuing (NCQ), command time-out and quality-of-service problems, SATATracker helps hard drive and storage OEMs systematically identify problems and optimize performance in SATA-based storage solutions. Designed for simple host to device configurations, the SATATracker Analyzer helps development engineers uncover problems that occur as a target device queues reorder the execution schedule of multiple pending commands.
Similar to a protocol analyzer, the SATATracker Analyzer taps into the data path between a host and device; but unlike a protocol analyzer it does not record bit-level details. Instead, it monitors all commands issued and tracks their completion, reporting details such as LBA, OP code and metrics such as command execution time and queue depth. The user may set a timeout trigger and the system will monitor all pending commands until any command exceeds the user-defined timeout, at which point the system will trigger and report the condition to the user. By capturing the exact sequence of events that preceded the time-out violation, validation engineers can determine which conditions effect command latency.
During the process of system integration, the user can initially set the timeout trigger to a large value to focus on commands that fail to complete and identify the associated hardware, programming or protocol errors. As these preliminary issues are resolved, the user can reduce the timeout trigger and focus on delayed and data-starved command conditions. This process systematically identifies problems and inefficiencies and allows users to optimize performance under different workloads.
The SATATracker is the first system capable of maintaining timing context and isolating command latency issues across complex transaction processing storage environments. It tracks every command issued between a host and device and independently times each operation. The SATATracker analyzer triggers in real time when it detects slow or incomplete commands. It displays a log of all operations with a marker at any timeout violation. This alone can save weeks of manual analysis by identifying the exact sequence of events that preceded the timeout condition.
The hidden cost of command latency
With new SAS and SATA based subsystems reaching the market, developers are learning first hand how difficult it is to isolate native command queuing problems across large subsystems. Random I/O operations (commonly associated with transaction processing) are more likely to stress device queue algorithms during periods of peak activity. It is here that subsystems that worked flawlessly at low link utilization rates may exhibit problems with stranded commands during periods of high disk activity.
The latest SATA-II disk drives make extensive use of command queuing to improve performance. Command queuing allows each target drive (typically a disk drive) to accept multiple commands into a “queue” and then reorder the commands to allow efficient completion of all commands. For example, if a drive head was positioned at sector A and was to pass through sectors B, C and D as the disk spins, commands received for data from sectors D, B, C and A would be reorganized and executed in the order A, B, C and D. The result is much faster completion of the total tasks required.
Commands that are acknowledged by a device but fail to complete or are slow to complete are surprisingly difficult to isolate. SATA-based disk drives configured in RAID environments aggravate the problem because they can generate burst data rates up 3Gbps. Even with maximum filtering techniques, these high data rates drastically reduce the amount of elapsed time that can be recorded with conventional analyzers.
The SATATracker Command Analyzer was designed to address precisely these problems. Whether used alone or in conjunction with a protocol analyzer, the SATATracker Analyzer allows the user to identify and systematically eliminate performance problems, resulting in a storage subsystem with optimum performance.
The log displays each operation with the Initiator, Target ID, and other command level parameters including LBA, OP Code and transfer length. Each entry includes an absolute timestamp and delta between Command and Status. It’s capable of maintaining a history of the last 8 million commands with markers at each time-out violation.
Economical and Upgradeable
The SATATracker Command Analyzer is built on the same hardware platform as LeCroy’s market leading SATracer 3G Protocol Analyzer for Serial ATA. The SATATracker system can be added to an existing LeCroy SATA protocol analyzer to provide a flexible multifunction test capability. LeCroy also offers a SAS Tracker for engineers focused on integrating Serial ATA within SAS-based storage subsystems. LeCroy’s SATracer protocol analyzer can be re-configured into a SATATracker command analyzer in the field as needed by users. Reconfiguring the system allows users to switch between the “bit-level” protocol analyzer and the “command” level tracker capability.
LeCroy’s storage analysis platform now provides the flexibility to evolve with the product development lifecycle. Equipment originally purchased for R&D test can be re-deployed in the field to help isolate marginal devices or software issues. But the real advantage of choosing LeCroy’s verification platform is its ability to shorten the time-to-market for SATA-based storage solutions.
