User Manual

Constellation.2 SAS Product Manual, Rev. K 22
Caution. The drive motor must come to a complete stop prior to changing the plane of operation. This time is
required to insure data integrity.
5.2.4 S.M.A.R.T.
S.M.A.R.T. is an acronym for Self-Monitoring Analysis and Reporting Technology. This technology is intended to recog-
nize conditions that indicate imminent drive failure and is designed to provide sufficient warning of a failure to allow
you to back up the data before an actual failure occurs.
Note. The drive’s firmware monitors specific attributes for degradation over time but can’t predict instanta-
neous drive failures.
Each monitored attribute has been selected to monitor a specific set of failure conditions in the operating perfor-
mance of the drive and the thresholds are optimized to minimize “false” and “failed” predictions.
Controlling S.M.A.R.T.
The operating mode of S.M.A.R.T. is controlled by the DEXCPT and PERF bits on the Informational Exceptions Control
mode page (1Ch). Use the DEXCPT bit to enable or disable the S.M.A.R.T. feature. Setting the DEXCPT bit disables all
S.M.A.R.T. functions. When enabled, S.M.A.R.T. collects on-line data as the drive performs normal read and write opera-
tions. When the PERF bit is set, the drive is considered to be in “On-line Mode Only” and will not perform off-line func-
tions.
You can measure off-line attributes and force the drive to save the data by using the Rezero Unit command. Forcing
S.M.A.R.T. resets the timer so that the next scheduled interrupt is in two hours.
You can interrogate the drive through the host to determine the time remaining before the next scheduled measure-
ment and data logging process occurs. To accomplish this, issue a Log Sense command to log page 0x3E. This allows
you to control when S.M.A.R.T. interruptions occur. Forcing S.M.A.R.T. with the RTZ command resets the timer.
Performance impact
S.M.A.R.T. attribute data is saved to the disk so that the events that caused a predictive failure can be recreated. The
drive measures and saves parameters once every two hours subject to an idle period on the drive interfaces. The pro-
cess of measuring off-line attribute data and saving data to the disk is uninterruptible. The maximum on-line only pro-
cessing delay is summarized below:
Reporting control
Reporting is controlled by the MRIE bits in the Informational Exceptions Control mode page (1Ch). Subject to the
reporting method, the firmware will issue to the host an 01-5Dxx sense code. The error code is preserved through bus
resets and power cycles.
Determining rate
S.M.A.R.T. monitors the rate at which errors occur and signals a predictive failure if the rate of degraded errors
increases to an unacceptable level. To determine rate, error events are logged and compared to the number of total
operations for a given attribute. The interval defines the number of operations over which to measure the rate. The
counter that keeps track of the current number of operations is referred to as the Interval Counter.
S.M.A.R.T. measures error rates. All errors for each monitored attribute are recorded. A counter keeps track of the num-
ber of errors for the current interval. This counter is referred to as the Failure Counter.
Maximum processing delay
On-line only delay
DEXCPT = 0, PERF = 1
Fully-enabled delay
DEXCPT = 0, PERF = 0
S.M.A.R.T. delay times 235 milliseconds 650 milliseconds