Hardware Reference
In-Depth Information
proper handling or sudden shock, or circuit failure (such as thermal-related solder prob-
lems or component failure).
S.M.A.R.T. was originally created by IBM in 1992. That year IBM began shipping 3
1/2-inchHDDsequippedwithPredictiveFailureAnalysis(PFA),anIBM-developedtech-
nology that periodically measures selected drive attributes and sends a warning message
when a predefined threshold is exceeded. IBM turned this technology over to the Amer-
ican National Standards Institute (ANSI) organization, and it subsequently became the
ANSI-standard S.M.A.R.T. protocol for SCSI drives, as defined in the ANSI-SCSI In-
formational Exception Control (IEC) document X3T10/94-190.
Interest in extending this technology to ATA drives led to the creation of the S.M.A.R.T.
Working Group in 1995. Besides IBM, other companies represented in the original group
were Seagate Technology, Conner Peripherals (now a part of Seagate), Fujitsu, Hewlett-
Packard, Maxtor (now a part of Seagate), Quantum (later merged with Maxtor), and
Western Digital. The S.M.A.R.T. specification produced by this group and placed in the
public domain covers both ATA and SCSI HDDs and can be found in most of the more
recently produced drives on the market.
The S.M.A.R.T. design of attributes and thresholds is similar in ATA and SCSI environ-
ments, but the reporting of information differs.
InanATAenvironment,driversoftwareonthesysteminterpretsthealarmsignalfromthe
drive generated by the S.M.A.R.T. “report status” command. The driver polls the drive
on a regular basis to check the status of this command and, if it signals imminent failure,
sends an alarm to the OS where it is passed on via an error message to the end user. This
structure also enables future enhancements, which might allow reporting of information
other than drive failure conditions. The system can read and evaluate the attributes and
alarms reported in addition to the basic “report status” command.
SCSI drives with S.M.A.R.T. communicate a reliability condition only as good or failing.
In a SCSI environment, the failure decision occurs at the disk drive and the host notifies
the user for action. The SCSI specification provides for a sense bit to be flagged if the
drive determines that a reliability issue exists. The system then alerts the end user via a
message.
NotethattraditionaldiskdiagnosticssuchasScandiskworkonlyonthedatasectorsofthe
disk surface and do not monitor all the drive functions that are monitored by S.M.A.R.T.
Most modern disk drives keep spare sectors available to use as substitutes for sectors that
have errors. When one of these spares is reallocated, the drive reports the activity to the
S.M.A.R.T.counterbutstilllookscompletelydefect-freetoasurfaceanalysisutility,such
as Scandisk.
