Seagate ST3300555SS, ST3146755SS, ST373355SS 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.

40	Cheetah T10 SAS Product Manual, Rev. A

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Contents Cheetah T10 SAS Page Contents Seagate Technology support services Defect and error managementInstallation Interface requirementsList of Figures Cheetah T10 SAS Product Manual, Rev. a Scope Cheetah T10 SAS disc driveCheetah T10 SAS Product Manual, Rev. a Electromagnetic compatibility Standards, compliance and reference documentsStandards Electromagnetic susceptibilityCompliance Reference documents Cheetah T10 SAS Product Manual, Rev. a General description Media description Standard featuresPerformance Formatted capacities Factory-installed accessoriesReliability Programmable drive capacityOptions factory installed User-installed accessoriesAccess time Performance characteristicsInternal drive characteristics Seek timeGeneral performance characteristics Format command execution time minutesStart/stop time Prefetch/multi-segmented cache control Cache operationCaching write data Prefetch operationRecoverable Errors Reliability specificationsError rates Unrecoverable ErrorsInterface errors Reliability and serviceSeek errors Preventive maintenanceControlling S.M.A.R.T Hot plugging the drive4 S.M.A.R.T Performance impactPredictive failures Reporting controlDetermining rate Thermal monitorReference Temperature Temperature Log Page 0DhPrimary Temperature Parameter Code DescriptionShort and extended tests State of the drive prior to testingInvoking DST Short test Function Code 001bShipping Product warrantyAbort Product repair and return informationCheetah T10 SAS Product Manual, Rev. a DC power requirements Physical/electrical specificationsAC power requirements ST3300555SS DC power requirementsST3146755SS Gbit mode Amps ST3146755SS DC power requirementsST373355SS DC power requirements ST373355SS Gbit mode AmpsConducted noise immunity General DC power requirement notesPower sequencing Current profilesTypical ST3300555SS drive current profiles Typical ST3146755SS drive current profiles Typical ST373355SS drive current profiles ST3300555SS in 3 Gbit operation Power dissipationST3300555SS in 1.5 Gbit operation ST3146755SS in 3 Gbit operation ST3146755SS in 1.5 Gbit operationST373355SS in 3 Gbit operation ST373355SS in 1.5 Gbit operationTemperature a. Operating Environmental limitsShock and vibration Relative humidityEffective altitude sea level a. Operating ShockPackage size Packaged/product weight Drop height Recommended mountingVibration a. Operating-normal Air cleanlinessCorrosive environment Mechanical specifications Acoustics Drive internal defects/errors Defect and error management Drive error recovery procedures Write retry count LBA cumulative, msec Background Media Scan SAS system errorsMedia Pre-Scan Deferred Auto-Reallocation Idle Read After WriteInstallation Drive orientationCooling Air flowDrive mounting GroundingCheetah T10 SAS Product Manual, Rev. a SAS features Interface requirementsDual port support Commands supported by Cheetah T10 SAS family drives Scsi commands supportedCommand name Command code Supported Commands supported by Cheetah T10 SAS family drives Commands supported by Cheetah T10 SAS family drives Commands supported by Cheetah T10 SAS family drives Cheetah T10 SAS inquiry data Mode Sense dataInquiry data Bytes Data hexPage ST3300555SS Mode Sense data Mode PagesST3146755SS Mode Sense data ST373355SS Mode Sense data Supported 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 1Impedance requirements Sheet 2 Transmitter characteristicsElectrical TxRx connections = -5,437dB Shows the zero-length test load Receiver characteristics Cheetah T10 SAS Product Manual, Rev. a Internet MySeagate Spp.seagate.com Seagate Technology support servicesWarranty Service Presales SupportData Recovery Services Authorized Service Centers Data Recovery ServicesCall center Presales and Technical Support Warranty Service FAX services-All Europe toll callToll-free support numbers Africa/Middle East support services Index NumericsPage SAS See also cooling Page Seagate Technology LLC