Seagate ST3146854LC, ST3146756SS (FDE) 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.

46	Cheetah 15K.6 SAS Product Manual, Rev. B

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Contents ST3146356SS ST3450856SSST3300656SS Page Contents Seagate Technology support services Defect and error managementInstallation Interface requirementsScope Model Number Full Disk Encryption FDECheetah 15K.6 SAS Product Manual, Rev. B Electromagnetic compatibility Standards, compliance and reference documentsStandards Electromagnetic susceptibilityCompliance European Union Restriction of Hazardous Substances RoHSReference documents Cheetah 15K.6 SAS Product Manual, Rev. B General description Performance Standard featuresMedia description Formatted capacities Factory-installed optionsReliability Programmable drive capacityCheetah 15K.6 SAS Product Manual, Rev. B Access time Performance characteristicsInternal drive characteristics Seek timeStart/stop time Format command execution time minutesGeneral performance characteristics 176 144 100Prefetch/multi-segmented cache control Cache operationCaching write data Prefetch operationRecoverable 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 MillisecondsPredictive failures Reporting controlDetermining rate Thermal monitorDrive Self Test DST Temperature Log Page 0Dh Parameter Code DescriptionState of the drive prior to testing DST failure definitionShort test Function Code 001b Invoking DSTShort and extended tests Extended test Function Code 010bShipping Product warrantyAbort Product repair and return informationCheetah 15K.6 SAS Product Manual, Rev. B DC power requirements Physical/electrical specificationsAC power requirements ST3450856SS DC power requirementsST3450056SS FDE Gbit mode Amps ST3450056SS FDE DC power requirementsST3300656SS DC power requirements ST3300656SS Gbit mode AmpsST3300056SS FDE Gbit mode Amps ST3300056SS FDE DC power requirementsST3146356SS DC power requirements ST3146356SS Gbit mode AmpsST3146756SS FDE DC power requirements ST3146756SS FDE Gbit mode AmpsCurrent profiles Power sequencingConducted noise immunity Typical 450GB current profiles Typical 146GB current profiles Power dissipation ST3450856SS modelST3450056SS FDE model ST3300656SS model ST3300056SS FDE model ST3146356SS model ST3146756SS FDE model in 3 Gbit operation Temperature Environmental limitsShock and vibration Relative humidityEffective altitude sea level ShockPackage size Packaged/product weight Drop height Recommended mountingAcoustics Air cleanlinessVibration Corrosive environmentMechanical specifications Physical dimensions Cheetah 15K.6 SAS Product Manual, Rev. B Drive error recovery procedures Defect and error management Drive internal defects/errors 51.87 Media Pre-Scan SAS system errorsBackground Media Scan Deferred Auto-Reallocation Idle Read After WriteCooling InstallationDrive orientation Air flow Drive mounting GroundingCheetah 15K.6 SAS Product Manual, Rev. B SAS features Interface requirementsDual port support Command name Command code Supported Scsi commands supportedCommands 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 Commands supported by Cheetah 15K.6 SAS family drives Inquiry data Bytes Data hexMode Sense data 2.1 ST3450856SS/ST3450056SS Mode Sense data Mode Pages2.2 ST3300656SS/ST3300056SS Mode Sense data 2.3 ST3146356SS/ST3146756SS Mode Sense data Miscellaneous status Miscellaneous operating features and conditionsMiscellaneous features SAS physical interfacePhysical 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 Compliant jitter test pattern Cjtpat Impedance specificationsReceiver jitter tolerance Impedance requirements Sheet 1Electrical TxRx connections Transmitter characteristicsImpedance requirements Sheet 2 = -5,437dB Shows the zero-length test load Receiver characteristics Cheetah 15K.6 SAS Product Manual, Rev. B Presales Support Seagate Technology support servicesInternet Technical SupportData Recovery Services Call Center Toll-free Direct dial Warranty ServiceData Recovery Services Authorized Service Centers Index NumericsIraw SAS See also cooling