Seagate ST3400755SS manual 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.

36	Cheetah NS SAS Product Manual, Rev. B

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Contents Cheetah NS SAS ST3400755SSPage Contents Seagate Technology support services Defect and error managementInstallation Interface requirementsList of Figures Typical ST3400755SS drive +5V and +12V current profilesCheetah NS SAS Product Manual, Rev. B Scope Cheetah NS SAS Product Manual, Rev. B Electromagnetic compatibility Standards, compliance and reference documentsStandards Electromagnetic susceptibilityCompliance Reference documents Cheetah NS SAS Product Manual, Rev. B General description Performance Standard featuresMedia description ReliabilityProgrammable drive capacity Factory-installed optionsFormatted capacities ST3400755SSCheetah NS SAS Product Manual, Rev. B Access time Performance characteristicsInternal drive characteristics Seek performanceFormat command execution time minutes General performance characteristicsStart/stop time Prefetch/multi-segmented cache control Cache operationCaching write data Prefetch operation Recoverable Errors Reliability specificationsError rates Unrecoverable ErrorsInterface errors Reliability and serviceSeek errors Preventive maintenancePerformance impact 4 S.M.A.R.TControlling S.M.A.R.T Reporting controlTemperature Log Page 0Dh Predictive failuresThermal monitor Implementation State of the drive prior to testingDST failure definition Invoking DSTExtended test Function Code 010b Product warrantyShort test Function Code 001b Log page entriesShipping Product repair and return informationCheetah NS SAS Product Manual, Rev. B DC power requirements Physical/electrical specificationsAC power requirements ST3400755SS DC power requirementsConducted noise immunity General DC power requirement notesPower sequencing Current profilesPower dissipation Typical ST3400755SS drive +5V and +12V current profilesTemperature Environmental limitsShock and vibration Relative humidityEffective altitude sea level ShockPackage size Packaged/product weight Drop height Recommended mountingAcoustics Air cleanlinessVibration Corrosive environmentX表示该部件（于同类物品程度上）所含的危险和有毒物质中国RoHS MCV标准所定义的门槛值。 China Restriction of Hazardous Substances RoHS DirectiveMechanical specifications Physical dimensionsCheetah NS SAS Product Manual, Rev. B Defect and error management Drive internal defects/errorsDrive error recovery procedures 77.87 SAS system errors Background Media ScanMedia Pre-Scan Deferred Auto-Reallocation Idle Read After WriteInstallation Drive orientationCooling Air flowDrive mounting GroundingCheetah NS SAS Product Manual, Rev. B SAS features Interface requirementsDual port support Scsi commands supported Commands supported by Cheetah NS SAS family drivesCommand name Command code Supported Commands supported by Cheetah NS SAS family drives Commands supported by Cheetah NS SAS family drives Commands supported by Cheetah NS SAS family drives Mode Sense data Inquiry dataCheetah NS SAS inquiry data Bytes Data hex Page 2.1 ST3400755SS Mode Sense data Mode PagesSupported Feature or condition Miscellaneous operating features and conditionsMiscellaneous features Miscellaneous statusSAS physical interface Datum B Physical characteristics Connector requirementsPin descriptions Pin Signal name Signal typeElectrical description SAS pin descriptionsSAS transmitters and receivers Signal characteristicsPower Ready LED OutGeneral interface characteristics LED drive signalDifferential signals Eye masks Eye masks overviewAbsolute amplitude Receive eye maskJitter tolerance masks Normalized time in UIJitter Peak-toSinusoidal Frequency in kHzTransmitter signal characteristics Signal characteristica Units GbpsMaximum allowable jitter Receiver signal characteristicsSignal characteristic Units Gbps Gbps m, n Deterministic jitterqCompliant jitter test pattern Cjtpat Impedance specificationsReceiver jitter tolerance Impedance requirements Sheet 1Transmitter characteristics Impedance requirements Sheet 2Electrical TxRx connections = -5,437dB Shows the zero-length test load Receiver characteristics Cheetah NS SAS Product Manual, Rev. B Presales Support Seagate Technology support servicesInternet Technical SupportWarranty Service Data Recovery Services Authorized Service CentersData Recovery Services Call Center Toll-free Direct dial Index NumericsPage SAS See also cooling