Seagate ST3400755SS manual SAS system errors, Background Media Scan, Media Pre-Scan

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7.3SAS system errors

Information on the reporting of operational errors or faults across the interface is given in the SAS Interface Manual. The SSP Response returns information to the host about numerous kinds of errors or faults. The Receive Diagnostic Results reports the results of diagnostic operations performed by the drive.

Status returned by the drive to the initiator is described in the SAS Interface Manual. Status reporting plays a role in systems error management and its use in that respect is described in sections where the various com- mands are discussed.

7.4Background Media Scan

Background Media Scan (BMS) is a self-initiated media scan. BMS is defined in the T10 document SPC-4 available from the T10 committee. BMS performs sequential reads across the entire pack of the media while the drive is idle. In RAID arrays, BMS allows hot spare drives to be scanned for defects prior to being put into service by the host system. On regular duty drives, if the host system makes use of the BMS Log Page, it can avoid placing data in suspect locations on the media. Unreadable and recovered error sites will be logged or reallocated per ARRE/AWRE settings.

With BMS, the host system can consume less power and system overhead by only checking BMS status and results rather than tying up the bus and consuming power in the process of host-initiated media scanning activ- ity.

Since the background scan functions are only done during idle periods, BMS causes a negligible impact to sys- tem performance. The first BMS scan for a newly manufactured drive is performed as quickly as possible to verify the media and protect data by setting the “Start time after idle” to 5ms, all subsequent scans begin after 500ms of idle time. Other features that normally use idle time to function will function normally because BMS functions for bursts of 800ms and then suspends activity for 100ms to allow other background functions to operate.

BMS interrupts immediately to service host commands from the interface bus while performing reads. BMS will complete any BMS-initiated error recovery prior to returning to service host-initiated commands. Overhead associated with a return to host-servicing activity from BMS only impacts the first command that interrupted BMS, this results in a typical delay of about 1 ms.

7.5Media Pre-Scan

Media Pre-Scan is a feature that allows the drive to repair media errors that would otherwise have been found by the host system during critical data accesses early in the drive’s life. The default setting for Media Pre-Scan is enabled on standard products. Media Pre-Scan checks each write command to determine if the destination LBAs have been scanned by BMS. If the LBAs have been verified, the drive proceeds with the normal write command. If the LBAs have not been verified by BMS, Pre-Scan will convert the write to a write verify to certify that the data was properly written to the disk.

Note. During Pre-Scan write verify commands, write performance may decrease by 50% until Pre-Scan completes. Write performance testing should be performed after Pre-Scan is complete. This may be checked by reading the BMS status.

To expedite the scan of the full pack and subsequently exit from the Pre-Scan period, BMS will begin scanning immediately when the drive goes to idle during the Pre-Scan period. In the event that the drive is in a high transaction traffic environment and is unable to complete a BMS scan within 24 power on hours BMS will dis- able Pre-Scan to restore full performance to the system.

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Contents ST3400755SS Cheetah NS SASPage Contents Installation Defect and error managementSeagate Technology support services Interface requirementsTypical ST3400755SS drive +5V and +12V current profiles List of FiguresCheetah NS SAS Product Manual, Rev. B Scope Cheetah NS SAS Product Manual, Rev. B Standards Standards, compliance and reference documentsElectromagnetic compatibility Electromagnetic susceptibilityCompliance Reference documents Cheetah NS SAS Product Manual, Rev. B General description Media description Standard featuresPerformance ReliabilityFormatted capacities Factory-installed optionsProgrammable drive capacity ST3400755SSCheetah NS SAS Product Manual, Rev. B Internal drive characteristics Performance characteristicsAccess time Seek performanceStart/stop time Format command execution time minutesGeneral performance characteristics Caching write data Prefetch/multi-segmented cache controlCache operation Prefetch operation Error rates Reliability specificationsRecoverable Errors Unrecoverable ErrorsSeek errors Reliability and serviceInterface errors Preventive maintenanceControlling S.M.A.R.T 4 S.M.A.R.TPerformance impact Reporting controlThermal monitor Temperature Log Page 0DhPredictive failures DST failure definition State of the drive prior to testingImplementation Invoking DSTShort test Function Code 001b Product warrantyExtended test Function Code 010b Log page entriesProduct repair and return information ShippingCheetah NS SAS Product Manual, Rev. B AC power requirements Physical/electrical specificationsDC power requirements ST3400755SS DC power requirementsPower sequencing General DC power requirement notesConducted noise immunity Current profilesTypical ST3400755SS drive +5V and +12V current profiles Power dissipationEnvironmental limits TemperatureEffective altitude sea level Relative humidityShock and vibration ShockRecommended mounting Package size Packaged/product weight Drop heightVibration Air cleanlinessAcoustics Corrosive environmentChina Restriction of Hazardous Substances RoHS Directive X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。Physical dimensions Mechanical specificationsCheetah NS SAS Product Manual, Rev. B Drive error recovery procedures Defect and error managementDrive internal defects/errors 77.87 Media Pre-Scan SAS system errorsBackground Media Scan Idle Read After Write Deferred Auto-ReallocationDrive orientation InstallationAir flow CoolingGrounding Drive mountingCheetah NS SAS Product Manual, Rev. B Interface requirements SAS featuresDual port support Command name Command code Supported Scsi commands supportedCommands supported by Cheetah NS SAS family drives Commands supported by Cheetah NS SAS family drives Commands supported by Cheetah NS SAS family drives Commands supported by Cheetah NS SAS family drives Cheetah NS SAS inquiry data Bytes Data hex Mode Sense dataInquiry data Page Mode Pages 2.1 ST3400755SS Mode Sense dataMiscellaneous features Miscellaneous operating features and conditionsSupported Feature or condition Miscellaneous statusSAS physical interface Datum B Connector requirements Physical characteristicsElectrical description Pin Signal name Signal typePin descriptions SAS pin descriptionsPower Signal characteristicsSAS transmitters and receivers Ready LED OutDifferential signals LED drive signalGeneral interface characteristics Eye masks Eye masks overviewJitter tolerance masks Receive eye maskAbsolute amplitude Normalized time in UISinusoidal Peak-toJitter Frequency in kHzSignal characteristica Units Gbps Transmitter signal characteristicsSignal characteristic Units Gbps Receiver signal characteristicsMaximum allowable jitter Gbps m, n Deterministic jitterqReceiver jitter tolerance Impedance specificationsCompliant 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 Cheetah NS SAS Product Manual, Rev. B Internet Seagate Technology support servicesPresales Support Technical SupportData Recovery Services Call Center Toll-free Direct dial Warranty ServiceData Recovery Services Authorized Service Centers Numerics IndexPage SAS See also cooling