Seagate ST3146356SS, ST3300656SS, ST3450856SS Deferred Auto-Reallocation, Idle Read After Write

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7.6Deferred Auto-Reallocation

Deferred Auto-Reallocation (DAR) simplifies reallocation algorithms at the system level by allowing the drive to reallocate unreadable locations on a subsequent write command. Sites are marked for DAR during read oper- ations performed by the drive. When a write command is received for an LBA marked for DAR, the auto-reallo- cation process is invoked and attempts to rewrite the data to the original location. If a verification of this rewrite fails, the sector is re-mapped to a spare location.

This is in contrast to the system having to use the Reassign Command to reassign a location that was unread- able and then generate a write command to rewrite the data. DAR is most effective when AWRE and ARRE are enabled—this is the default setting from the Seagate factory. With AWRE and ARRE disabled DAR is unable to reallocate the failing location and will report an error sense code indicating that a write command is being attempted to a previously failing location.

7.7Idle Read After Write

Idle Read After Write (IRAW) utilizes idle time to verify the integrity of recently written data. During idle periods, no active system requests, the drive reads recently written data from the media and compares it to valid write command data resident in the drives data buffer. Any sectors that fail the comparison result in the invocation of a rewrite and auto-reallocation process. The process attempts to rewrite the data to the original location. If a verification of this rewrite fails, the sector is re-mapped to a spare location.

42	Cheetah 15K.6 SAS Product Manual, Rev. A

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Contents Cheetah 15K.6 SAS ST3450856SS ST3300656SS ST3146356SSPage Contents Defect and error management InstallationSeagate Technology support services Interface requirementsList of Figures Cheetah 15K.6 SAS disk driveCheetah 15K.6 SAS Product Manual, Rev. a Scope Cheetah 15K.6 SAS disk driveCheetah 15K.6 SAS Product Manual, Rev. a Standards, compliance and reference documents StandardsElectromagnetic compatibility Electromagnetic susceptibilityCompliance European Union Restriction of Hazardous Substances RoHSReference documents Cheetah 15K.6 SAS Product Manual, Rev. a General description Standard features Media descriptionPerformance Factory-installed accessories Options factory installedReliability Formatted capacitiesCheetah 15K.6 SAS Product Manual, Rev. a Performance characteristics Internal drive characteristicsAccess time Seek timeFormat command execution time minutes General performance characteristicsStart/stop time Prefetch/multi-segmented cache control Cache operationCaching write data Prefetch operationReliability specifications Error ratesRecoverable Errors Unrecoverable ErrorsReliability and service Seek errorsInterface errors Preventive maintenance4 S.M.A.R.T Controlling S.M.A.R.TPerformance impact MillisecondsReporting control Determining ratePredictive failures Thermal monitorTemperature Log Page 0Dh Primary TemperatureReference Temperature Parameter Code DescriptionState of the drive prior to testing Invoking DSTShort and extended tests Short test Function Code 001bProduct warranty AbortShipping Product repair and return informationCheetah 15K.6 SAS Product Manual, Rev. a Physical/electrical specifications AC power requirementsDC power requirements ST3450856SS DC power requirementsST3300656SS DC power requirements ST3146356SS DC power requirementsST3300656SS Gbit mode Amps ST3146356SS Gbit mode AmpsGeneral DC power requirement notes Power sequencingConducted noise immunity Current profilesTypical ST3450856SS current profiles Typical ST3300656SS current profiles Typical ST3146356SS current profiles Power dissipation ST3450856SS in 3 Gbit operationST3300656SS CURRENT/POWER vs Throughput SAS 3.0GB ST3300656SS in 3 Gbit operationST3146356SS CURRENT/POWER vs Throughput SAS 3.0GB ST3146356SS in 3 Gbit operationRandom 8 Block Reads Temperature Environmental limitsRelative humidity Effective altitude sea levelShock and vibration ShockPackage size Packaged/product weight Drop height Recommended mountingAir cleanliness VibrationAcoustics Corrosive environmentMechanical specifications Physical dimensions Cheetah 15K.6 SAS Product Manual, Rev. a Defect and error management Drive internal defects/errorsDrive error recovery procedures 51.87 SAS system errors Background Media ScanMedia Pre-Scan Deferred Auto-Reallocation Idle Read After WriteInstallation Drive orientationCooling Air flowDrive mounting GroundingCheetah 15K.6 SAS Product Manual, Rev. a SAS features Interface requirementsDual port support Scsi commands supported Commands supported by Cheetah 15K.6 SAS family drivesCommand name Command code Supported Commands supported by Cheetah 15K.6 SAS family drives Commands supported by Cheetah 15K.6 SAS family drives Commands supported by Cheetah 15K.6 SAS family drives Mode Sense data Inquiry dataBytes Data hex Page 2.1 ST3450856SS Mode Sense data Mode Pages2.2 ST3300656SS Mode Sense data 2.3 ST3146356SS Mode Sense data Miscellaneous operating features and conditions Miscellaneous featuresSupported Feature or condition Miscellaneous statusSAS physical interface Datum B Physical characteristics Connector requirementsPin Signal name Signal type Electrical descriptionPin descriptions SAS pin descriptionsSignal characteristics PowerSAS transmitters and receivers Ready LED OutLED drive signal Differential signalsGeneral interface characteristics Eye masks Eye masks overviewReceive eye mask Jitter tolerance masksAbsolute amplitude Normalized time in UIPeak-to SinusoidalJitter Frequency in kHzTransmitter signal characteristics Signal characteristica Units GbpsReceiver signal characteristics Signal characteristic Units GbpsMaximum allowable jitter Gbps m, n Deterministic jitterqImpedance specifications Receiver jitter toleranceCompliant jitter test pattern Cjtpat Impedance requirements Sheet 1Transmitter characteristics Impedance requirements Sheet 2Electrical TxRx connections = -5,437dB Shows the zero-length test load Receiver characteristics Cheetah 15K.6 SAS Product Manual, Rev. a Seagate Technology support services InternetPresales Support Technical SupportWarranty Service Data Recovery Services Authorized Service CentersData Recovery Services Call Center Toll-free Direct dial Index NumericsPage SAS See also cooling