Seagate ST31000640SSIM 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.

38	Barracuda ES.2 SAS Product Manual, Rev. G

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Contents Barracuda ES.2 SAS ST31000640SS ST3750630SS ST3500620SSPage Performance characteristics Reliability specificationsPhysical/electrical specifications General descriptionInterface requirements Defect and error managementInstallation Seagate Technology Support Services Barracuda ES.2 SAS Product Manual, Rev Scope Barracuda ES.2 SAS Product Manual, Rev. G Standards, compliance and reference documents StandardsElectromagnetic compatibility Electromagnetic susceptibilityCompliance Reference documents Barracuda ES.2 SAS Product Manual, Rev. G General description Barracuda ES.2 drive illustrationStandard features Media descriptionPerformance ReliabilityProgrammable drive capacity Factory-installed optionsFormatted capacities Barracuda ES.2 SAS Product Manual, Rev. G Performance characteristics Internal drive characteristicsAccess time Seek performanceStart/stop time Format command execution time minutesGeneral performance characteristics Caching write data Prefetch/multi-segmented cache controlCache operation Prefetch operation Reliability 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 Reporting controlThermal monitor Temperature Log Page 0DhPredictive failures State of the drive prior to testing DST failure definitionImplementation Invoking DSTProduct warranty Short test Function Code 001bExtended test Function Code 010b Log page entriesShipping Product repair and return informationBarracuda ES.2 SAS Product Manual, Rev. G Physical/electrical specifications AC power requirementsDC power requirements ST31000640SS DC power requirementsST3750630SS DC power requirements ST3500620SS DC power requirementsGeneral DC power requirement notes Power sequencingConducted noise immunity Current profilesTypical ST31000640SS drive +5V and +12V current profiles Power dissipation Typical ST3500620SS drive +5V and +12V current profilesBarracuda ES.2 SAS Product Manual, Rev. G Temperature a. Operating Environmental limitsRelative humidity Effective altitude sea level a. OperatingShock and vibration ShockPackage size Packaged/product weight Drop height Air cleanliness Vibration a. Operating-normalAcoustics Corrosive environmentSee Section Barracuda ES.2 SAS Product Manual, Rev. G Mechanical specifications Physical dimensionsDrive error recovery procedures Defect and error managementDrive internal defects/errors 108.29 Media Pre-Scan SAS system errorsBackground Media Scan Deferred Auto-Reallocation Idle Read After WriteInstallation Drive orientationCooling Air flowDrive mounting GroundingBarracuda ES.2 SAS Product Manual, Rev. G SAS features Interface requirementsDual port support Command name Command code Supported Scsi commands supportedCommands supported by Barracuda ES.2 SAS family drives Commands supported by Barracuda ES.2 SAS family drives Commands supported by Barracuda ES.2 SAS family drives Commands supported by Barracuda ES.2 SAS family drives Barracuda ES.2 SAS inquiry data Bytes Data hex Mode Sense dataInquiry data Page 2.1 ST31000640SS Mode Sense data Mode Pages2.2 ST3750630SS Mode Sense data 2.3 ST3500620SS 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 1Electrical TxRx connections Transmitter characteristicsImpedance requirements Sheet 2 = -5,437dB Shows the zero-length test load Receiver characteristics Barracuda ES.2 SAS Product Manual, Rev. G