Disk-Drive Enclosure Testing

Disk-drive performance is dependent upon the enclosure and mounting system, and these factors can enhance or reduce overall system performance. Two key factors are rotational vibration and operating temperature. Rotational vibration introduces additional error into the servo tracking system. As the error rate increases the disk drive must spend more time in error recovery, thus reducing the end performance. Elevated temperatures also reduce error rate margin and degrade performance. These effects on system performance need to be understood during the development period, and certainly prior to delivery to end customers. RTS has specific test methodologies to determine the efficacy of the system enclosure with respect to vibration and temperature hot spots.

Rotational Vibration Testing

Vibration issues can be introduced from poorly- balanced disk-drive spindles, from the seeking forces of adjacent drives, and from the coupling effects introduced within the system enclosure. Disk-drive manufacturers can design specific features into their drives, such as dual-plane balancing of the spindle assembly to reduce the RRO (Repeatable Run Out). However, the specific system enclosure and drive-mounting schemes will have a significant effect upon the drive performance. The drive mounting and enclosure can affect the coupled energy and either enhance or dampen the effects.

When a seek is initiated, the accelerating force causes the drive to torque around a central point - the result is the drive attempts to spin in a circular motion. This energy can be coupled into adjacent drives, increasing error rates and inducing error-recovery algorithms. This causes an increase in on-the-fly ECC activities and in missed revolutions. Other components mounted in the system enclosure can contribute to vibration, such as fans and CD-ROMS. The overall system performance is affected by the specific disk drives, the enclosure and the drive-mounting configuration.

RTS provides a full characterization of drive performance in the specified system enclosure. IOmeter and the System Test Exerciser are run with all drives at idle to establish a baseline. These measurements are repeated with seek activity from all adjacent drives. The results are plotted, showing the relationship between the fixture, the enclosure and each drive slot at seeking versus idle. This provides a complete baseline that can be used to drive changes in the system enclosure/mounting configurations, the disk drive, or to simply provide a guideline for the end user.

Components Required

Depending upon the requested test, the customer can supply the disk drive enclosure, the disk drives, the relevant manuals, and any customer-unique tests. RTS can provide the test monitoring equipment, the operating systems, the generic test software, and a fixture for the out-of-enclosure testing. RTS can supply the enclosure if drive-only testing is required, or RTS can provide the disk drives if only enclosure testing is required. However, to provide the most accurate representation of field installations, the ideal model is to test the enclosure with the drives that are specified for the end system.

The test schedule is dependent upon the amount and level of testing required. The rotational vibration test time for a single enclosure with up to 6 slots is typically 1 week, including the written test report. Enclosures with up to 14 slots will take approximately 2 weeks. Test times can be extended if problems are encountered, to allow time for the investigation and problem analysis.

The thermal testing, including the test report, is typically 1 week for a single enclosure with up to 6 slots and 2 weeks for up to 14 slots.

Thermal Management Testing

The operating temperature range is specified for disk drives to assure the reliability and performance is maintained. Temperature affects system margins in the servo, read/write electronics, head fly height, and the magnetic performance of the media. For example, the magnetic coercivity of the media decreases with temperature, which reduces the read signal and increases error recovery activity.

The disk-drive manufacturer typically specifies the airflow and operating temperature range. Airflow and case temperature are used to determine if an enclosure is supplying adequate cooling to all disk drives. Meeting the specifications for each drive in the system can be challenging, because even the best cooling systems with multiple fans can have hot spots. These hot spots can cause specific components to operate near the outer margins, or worst case, to exceed the specified temperature range.

RTS maps every drive in the enclosure with respect to airflow and temperature over varying conditions of drive operation. This provides a complete picture for understanding the airflow and cooling within the enclosure.

Test Reports

A test report is provided at the conclusion of the testing. The report includes all test data, graphs, and analysis of problems with recommendations for corrective actions. Verbal updates are provided as the work progresses and when problems are encountered. This allows the customer the opportunity to discuss the problems and either request additional testing or halt the testing until modifications are completed.

Testing Procedures

The rotational vibration testing is measured in three situations:

• Test drive in a separate fixture
• Drive measured in the enclosure with all neighboring drives at idle
• Drive measured in the enclosure with all neighboring drives seeking

Thermal testing is measured at four specific intervals:

• Power on ambient to idle temperature
• 50% duty cycles for 2 hours
• 100% duty cycle for 2 hours
• 100% duty cycle to idle and dwell at idle for 1 hour

This testing provides the drive baseline, along with the best and worse case situations for both vibration and temperature inside the enclosure. Graphs illustrating vibration-testing results are shown in figures 1 and 2. Graphs illustrating thermal-testing results are shown in figures 3 and 4.

Conclusion

System designers, builders, and integrators need to understand the effects of vibration and temperature on system performance. Ideally, these effects should be understood during the system development phase so that changes can be incorporated to address any issues. However, it is also important to understand any limitations and restrictions in the final system before delivery to the end customers.

RTS has the capability, experience and facilities to accomplish this testing, all at very reasonable costs.

Figure 1: Rotational Vib - I/Os per sec	Figure 3: Temp Profile vs Slot
Figure 2: Rotational Vib - Data Throughput	Figure 4: Temp Profile vs Time
Let RTS characterize your disk drives in your enclosure Independent lab evaluation Full understanding of performance within your system Recommendations for improvements in drive mounting and cooling Economical testing

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