Specifications

SCSI to SATA RAID Subsystem | Administrator’s Manual S.M.A.R.T. Configuration | en 179
Bosch Security Systems F.01U.027.802 | V1 | 2006.11
12.3 S.M.A.R.T. (Self-Monitoring, Analysis and Reporting
Technology)
This section provides a brief introduction to S.M.A.R.T. as one way to predict drive failure and
Bosch’s implementations with S.M.A.R.T. for preventing data loss caused by drive failure.
Introduction
Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.) is an emerging technology
that provides near-term failure prediction for disk drives. When S.M.A.R.T. is enabled, the
drive monitors predetermined disk drive attributes that are susceptible to degradation over
time.
If a failure is likely to occur, S.M.A.R.T. makes a status report available so that the host can
prompt the user to backup data from the failing drive. However, not all failures can be pre-
dicted. S.M.A.R.T. predictions are limited to the attributes the drive can monitor which are
selected by the device manufacturer based on the attribute’s ability to contribute to predict
degrading or fault conditions.
Although attributes are drive specific, a variety of typical characteristics can be identified:
• Head flying height
• Data throughput performance
• Spin-up time
• Re-allocated sector count
• Seek error rate
• Seek time performance
• Spin try recount
• Drive calibration retry count
Drives with reliability prediction capability only indicate whether the drive is “good” or “fail-
ing.” In a SCSI environment, the failure decision occurs on the disk drive and the host notifies
the user for action. The SCSI specification provides a sense bit to be flagged if the disk drive
determines that a reliability issue exists. The system then alerts the user/system administra-
tor.
Bosch's Implementations with S.M.A.R.T.
Bosch uses the ANSI-SCSI Informational Exception Control (IEC) document X3T10/94-190
standard.
There are four selections related to the S.M.A.R.T. functions in firmware:
1. Disabled
Disables S.M.A.R.T.-related functions
2. Detect Only:
When the S.M.A.R.T. function is enabled, the controller will send a command to enable all
drives' S.M.A.R.T. function, if a drive predicts a problem, the controller will report the
problem in an event log.
3. Detect and Perpetual Clone
When the S.M.A.R.T. function is enabled, the controller will send a command to enable all
drives' S.M.A.R.T. function. If a drive predicts a problem, the controller will report the
problem in an event log. The controller will clone the drive if a Dedicated/Global spare is
available. The drive with predicted errors will not be taken off-line, and the clone drive
will still act as a standby drive.
If the drive with predicted errors fails, the clone drive will take over immediately. If the
problematic drive is still working and another drive in the same logical drive fails, the
clone drive will resume the role of a standby spare and start to rebuild the failed drive
immediately. This prevents a fatal drive error if yet another drive should fail.