Seagate ST3300955FC, ST3400755FC manual Prefetch operation

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If read caching is enabled (RCD=0), then data written to the medium is retained in the cache to be made avail- able for future read cache hits. The same buffer space and segmentation is used as set up for read functions. The buffer segmentation scheme is set up or changed independently, having nothing to do with the state of RCD. When a write command is issued, if RCD=0, the cache is first checked to see if any logical blocks that are to be written are already stored in the cache from a previous read or write command. If there are, the respective cache segments are cleared. The new data is cached for subsequent Read commands.

If the number of write data logical blocks exceed the size of the segment being written into, when the end of the segment is reached, the data is written into the beginning of the same cache segment, overwriting the data that was written there at the beginning of the operation; however, the drive does not overwrite data that has not yet been written to the medium.

If write caching is enabled (WCE=1), then the drive may return Good status on a write command after the data has been transferred into the cache, but before the data has been written to the medium. If an error occurs while writing the data to the medium, and Good status has already been returned, a deferred error will be gen- erated.

The Synchronize Cache command may be used to force the drive to write all cached write data to the medium. Upon completion of a Synchronize Cache command, all data received from previous write commands will have been written to the medium.

Tables 17 and 18 show the mode default settings for these drives.

4.5.2Prefetch operation

If the Prefetch feature is enabled, data in contiguous logical blocks on the disc immediately beyond that which was requested by a Read command are retrieved and stored in the buffer for immediate transfer from the buffer to the host on subsequent Read commands that request those logical blocks (this is true even if cache operation is disabled). Though the prefetch operation uses the buffer as a cache, finding the requested data in the buffer is a prefetch hit, not a cache operation hit.

To enable Prefetch, use Mode Select page 08h, byte 12, bit 5 (Disable Read Ahead - DRA bit). DRA bit = 0 enables prefetch.

The drive does not use the Max Prefetch field (bytes 8 and 9) or the Prefetch Ceiling field (bytes 10 and 11).

When prefetch (read look-ahead) is enabled (enabled by DRA = 0), the drive enables prefetch of contiguous blocks from the disc when it senses that a prefetch hit will likely occur. The drive disables prefetch when it decides that a prefetch hit is not likely to occur.

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Cheetah NS FC Product Manual, Rev. A

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Contents Cheetah NS FC ST3400755FC ST3300955FCPage Cheetah NS FC Product Manual, Rev. a Cheetah NS FC Product Manual, Rev. a Contents Defect and error management InstallationInterface requirements Seagate Technology support services Cheetah NS FC Product Manual, Rev. a List of Figures Page Scope Cheetah NS FC Product Manual, Rev. a Standards, compliance and reference documents StandardsElectromagnetic compatibility Electromagnetic susceptibilityCompliance Reference documents Ncits TR-19Cheetah NS FC Product Manual, Rev. a General description Standard features Media descriptionPerformance ReliabilityFormatted capacities Programmable drive capacityFactory-installed options User-installed accessoriesPerformance characteristics Internal drive characteristicsAccess time Seek performanceFormat command execution time minutes General performance characteristicsStart/stop time Prefetch/multi-segmented cache control Cache operationCaching write data 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 MillisecondsReporting control Determining ratePredictive failures Thermal monitorState of the drive prior to testing Parameter Code DescriptionDrive Self Test DST DST failure definitionInvoking DST Short and extended testsShort test Function Code 001b Extended test Function Code 010bProduct warranty AbortShipping Product repair and return informationCheetah NS FC Product Manual, Rev. a Physical/electrical specifications AC power requirementsDC power requirements DC power requirements for ST3400755FC model Gbit AmpsGeneral DC power requirement notes DC power requirements for ST3300955FC model Gbit AmpsPower sequencing Conducted noise immunityCurrent profiles Cheetah NS FC Product Manual, Rev. a Power dissipation ST3400755 CURRENT/POWER vs Throughput FC 4GBST3400755FC Random 8 Block ReadsST3300955 CURRENT/POWER vs Throughput FC 4GB ST3300955FCTemperature Environmental limitsRelative humidity Package size Packaged/product weight Drop height Effective altitude sea levelShock and vibration ShockRecommended mounting Air cleanliness VibrationAcoustics 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 Mounting configuration dimensionsCheetah NS FC Product Manual, Rev. a Defect and error management Drive internal defects/errorsDrive error recovery procedures 77.87 FC-AL system errors Background Media ScanMedia Pre-Scan Deferred Auto-Reallocation Idle Read After WriteInstallation Drive ID/option selectionDrive orientation CoolingDrive mounting Air flowGrounding Cheetah NS FC Product Manual, Rev. a FC-AL features Fibre Channel link service framesLink services supported Type of frame Interface requirementsFibre Channel task management functions Fibre Channel task management responsesFC Scsi FCP response codes Function name Response code Fibre Channel port login NPort login Plogi payload BytesFibre Channel port login accept Fibre Channel Process LoginNPort Login Accept ACC payload Bytes Process Login Plri payloadFibre Channel Process Login Accept Fibre Channel fabric loginProcess Login Accept ACC payload Bytes Fabric Login Flogi payload BytesFibre Channel fabric accept login Fabric Login Accept ACC payload BytesDual port support Fibre Channel Arbitrated Loop optionsFC-AL options supported Option SupportedScsi commands supported Supported commands Command code Command nameVerify error recovery page 07h Cheetah NS FC Product Manual, Rev. a Temperature page 0Dh Mode Sense data Inquiry dataCheetah NS FC inquiry data Bytes Data hex Page Mode Sense 10 Byte Header Data Mode Data Header Miscellaneous operating features and conditions Miscellaneous featuresSupported Feature or condition Miscellaneous statusPhysical characteristics FC-AL physical interfacePhysical description Connector requirements Electrical descriptionPin descriptions FC-SCA pin descriptions Pin Signal name Signal type Pin Signal name Signal typeFC-AL transmitters and receivers Power Fault LED OutEnable port bypass signals Active LED OutMotor start controls Parallel Enclosure Services Interface ESI 11 SEL6 through SEL0 ID linesSetting Arbitrated loop physical address Alpa valuesHex Dec Signal characteristics TTL input characteristicsDevice control codes LED driver signals FC Differential outputFC Differential input Receive eye diagram Eye diagram data values Link rate GHz Seagate Technology support services InternetPresales Support Technical SupportWarranty Service Data Recovery Services Authorized Service CentersData Recovery Services Call Center Toll-free Direct dial Index NumericsFAN Flogi Plogi SEL ID See also cooling
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