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18 Constellation.2 SAS Product Manual, Rev. H
S.M.A.R.T. measures error rates. All errors for each monitored attribute are recorded. A counter keeps track of
the number of errors for the current interval. This counter is referred to as the Failure Counter.
Error rate is the number of errors per operation. The algorithm that S.M.A.R.T. uses to record rates of error is to
set thresholds for the number of errors and their interval. If the number of errors exceeds the threshold before
the interval expires, the error rate is considered to be unacceptable. If the number of errors does not exceed
the threshold before the interval expires, the error rate is considered to be acceptable. In either case, the inter-
val and failure counters are reset and the process starts over.
Predictive failures
S.M.A.R.T. signals predictive failures when the drive is performing unacceptably for a period of time. The firm-
ware keeps a running count of the number of times the error rate for each attribute is unacceptable. To accom-
plish this, a counter is incremented each time the error rate is unacceptable and decremented (not to exceed
zero) whenever the error rate is acceptable. If the counter continually increments such that it reaches the pre-
dictive threshold, a predictive failure is signaled. This counter is referred to as the Failure History Counter.
There is a separate Failure History Counter for each attribute.
6.2.5 Thermal monitor
Constellation.2 drives implement a temperature warning system which:
1. Signals the host if the temperature exceeds a value which would threaten the drive.
2. Signals the host if the temperature exceeds a user-specified value.
3. Saves a S.M.A.R.T. data frame on the drive which exceeds the threatening temperature value.
A temperature sensor monitors the drive temperature and issues a warning over the interface when the tem-
perature exceeds a set threshold. The temperature is measured at power-up and then at ten-minute intervals
after power-up.
The thermal monitor system generates a warning code of 01-0B01 when the temperature exceeds the speci-
fied limit in compliance with the SCSI standard. The drive temperature is reported in the FRU code field of
mode sense data. You can use this information to determine if the warning is due to the temperature exceeding
the drive threatening temperature or the user-specified temperature.
This feature is controlled by the Enable Warning (EWasc) bit, and the reporting mechanism is controlled by the
Method of Reporting Informational Exceptions field (MRIE) on the Informational Exceptions Control (IEC)
mode page (1Ch).
The current algorithm implements two temperature trip points. The first trip point is set at 68°C. The second trip
point is user-selectable using the Log Select command. The reference temperature parameter in the tempera-
ture log page (see Table 1) can be used to set this trip point. The default value for this drive is 68°C, however,
you can set it to any value in the range of 0 to 68°C. If you specify a temperature greater than 68°C in this field,
the temperature is rounded down to 68°C. A sense code is sent to the host to indicate the rounding of the
parameter field.
Table 1: Temperature Log Page (0Dh)
Parameter Code Description
0000h
Primary Temperature
0001h
Reference Temperature