IBM C2B 2.25 Brick On Sled carrier 128-pin HPC - Manual (Page 48)

USER RESPONSIBLE F O R V E R I F Y I N G VERSION A N D COMPLETENESS
O E M F U N C T I O N A L SPECIFICATION ULTRASTAR X P (DFHC) SSA M O D E L S 1.12/2.25 GB - 1.0" H I G H
3.6.1 Servo Run Out Measurements
The drive periodically measures servo run out, the amount of wobble on each disk, to track follow more
precisely.
Servo run out for all heads is measured every 60 minutes, therefore the frequency of run out measurements is
dependent on the number of heads a particular model has. The drive attempts to spread the measurements
evenly in time and each measurement takes 100 milliseconds. For example, a model C4x with 8 heads per-
forms one run out measurement every 7 1/2 minutes (60 / 8).
3.6.2 Servo Bias Measurements
The drive periodically measures servo bias, the amount of resistance to head movement as a function of disk
radius. It also helps prevent disk lubrication migration by moving the heads over the entire disk surface.
Servo bias is measured every 12 minutes during the first hour after a power cycle, and every 60 minutes after
that. The measurement takes 200 milliseconds.
3.6.3 Predictive Failure Analysis
Predictive Failure Analysis measures drive parameters and can predict if a drive failure is imminent.
Eight different P F A measurements are taken for each head. All measurements for all heads are taken over a
period of 4 hours, therefore the frequency of P F A is dependent on the number of heads a particular model
has. The drive attempts to spread the measurements evenly in time and each measurement takes about 80
milliseconds.
For example, a C4x model with 8 heads will perform one P F A measurement every 3.7
minutes (240 / 8 × 8). For the last head tested for a particular measurement type (once every 1/2 hour), the
data is analyzed and stored.
The extra execution time for those occurrences is approximately 40 millisec-
onds.
This measurement/analysis feature can be disabled for critical response time periods of operation by setting
the Page 0h Mode Parameter L I T F =
1. The using system also has the option of forcing execution at
known times by issuing the Rezero Unit command if the Page 0h Mode Parameter T C C = 1. All tests for
all heads occur at those times.
Note: Refer to the Ultrastar XP ( D F H C ) S S A Models Interface Specification for more details about PFA,
LITF, and TCC.
3.6.4 Channel Calibration
The drive periodically calibrates the channel to insure that the read and write circuits function optimally,
thus reducing the likelihood of soft errors.
Channel calibration is done once every 4 hours and typically completes in 20 milliseconds, but may take up
to 64 milliseconds per measurement.
The measurement will only be started if the drive has not received a command for at least 5 seconds. This
means that multiple commands are accepted and executed without delay if the commands are received by the
drive within 5 seconds after the completion of a previous command.
This function also makes use of the
mechanism to alter the idle detection period to limit execution for critical response time periods of operation,
if needed.
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