Seagate ST3300457FC, ST3300557FC, ST3300657FC, ST3450857FC Caching write data, Prefetch operation

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5.5.1Caching write data

Write caching is a write operation by the drive that makes use of a drive buffer storage area where the data to be written to the medium is stored while the drive performs the Write command.

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.

Table 18 shows the mode default settings for the drive.

5.5.2Prefetch 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 buf- fer 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.

Cheetah 15K.7 FC Product Manual, Rev. C

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Contents Standard models Self-Encrypting Drive models ST3600857FC ST3450657FC ST3300457FCSED Fips 140-2 models Page Contents Interface requirements Defect and error managementInstallation About Fips About self-encrypting drivesCheetah 15K.7 FC Product Manual, Rev. C Iii Cheetah 15K.7 FC Product Manual, Rev. C Seagate Online Support and Services Seagate Technology support servicesScope Electromagnetic susceptibility Applicable standards and reference documentationStandards Electromagnetic compatibilityEuropean Union Restriction of Hazardous Substances RoHS Ncits TR-20 Reference documentsGeneral description Standard features Formatted capacities Media descriptionPerformance ReliabilityUser-installed accessories Factory-installed optionsProgrammable drive capacity Access time Performance characteristics Internal drive characteristics Seek performance characteristicsST3600057FC ST3450857FC ST3300657FC Format command execution time minutesGeneral performance characteristics Start/stop timeCache operation Prefetch/multi-segmented cache controlPrefetch operation Caching write dataUnrecoverable Errors Reliability specificationsError rates Recoverable ErrorsPreventive maintenance Reliability and serviceSeek errors Interface errorsMilliseconds 4 S.M.A.R.TControlling S.M.A.R.T Performance impactThermal monitor Temperature Log Page 0DhDetermining rate Predictive failuresImplementation State of the drive prior to testingDrive Self Test DST DST failure definitionLog page entries Short and extended testsShort test Function Code 001b Extended test Function Code 010bShipping Product warrantyProduct repair and return information AC power requirements Physical/electrical specificationsDC power requirements ST3450857FC DC power requirements Gbit Amps ST3600057FC DC power requirements Gbit AmpsST3300657FC DC power requirements Gbit Amps General DC power requirement notesConducted noise immunity Power sequencingCurrent profiles Typical ST3450857FC current profiles Typical ST3300657FC current profiles 600GB model Power dissipation450GB models Environmental limits Temperature a. Operating300GB models Effective altitude sea level a. Operating Relative humidityShock and vibration Package size Packaged/product weight Drop heightShock Recommended mounting Vibration a. Operating-normal Air cleanlinessAcoustics RoHS compliance statement Corrosive environmentElectromagnetic susceptibility See Section Mounting configuration dimensions Mechanical specificationsPurpose About FipsLevel 2 security Data encryption Controlled accessAdmin SP About self-encrypting drivesData bands Default passwordRandom number generator RNG Drive lockingCryptographic erase Authenticated firmware downloadPower requirements Supported commandsDrive internal defects/errors Defect and error managementDrive error recovery procedures Page These values are subject to change FC-AL system errorsMedia Pre-Scan Background Media ScanDeferred Auto-Reallocation Idle Read After Write Drive ID/option selection InstallationDrive orientation Air flow CoolingGrounding Drive mountingInterface requirements FC-AL featuresFibre Channel link service frames Link services supported Type of frameFibre Channel task management responses Fibre Channel task management functionsFC Scsi FCP response codes Function name Response code NPort login Plogi payload Bytes Fibre Channel port loginNPort Login Accept ACC payload Bytes Fibre Channel port login acceptProcess Login Plri payload Fabric Login Flogi payload Bytes Fibre Channel Process Login AcceptFibre Channel fabric login Process Login Accept ACC payload BytesFabric Login Accept ACC payload Bytes Fibre Channel fabric accept loginFC-AL options supported Scsi commands supportedDual port support Fibre Channel Arbitrated Loop optionsSupported commands Cheetah 15K.7 FC Product Manual, Rev. C Cheetah 15K.7 FC Product Manual, Rev. C Background Medium Scan 15h Inquiry data Mode Sense dataCheetah 15K.7 FC inquiry data Bytes Data hex Page Mode Data Header Block Descriptor Ec b2 5c 00 00 02 Miscellaneous status Miscellaneous operating features and conditionsMiscellaneous features Supported Feature or conditionFC-AL physical interface Physical characteristicsPhysical description Electrical description Connector requirementsPin descriptions Pin Signal name Signal type FC-SCA pin descriptions Pin Signal name Signal typeFC-AL transmitters and receivers Fault LED Out PowerActive LED Out Enable port bypass signalsMotor start controls 12.5.11 SEL6 through SEL0 ID lines Parallel Enclosure Services Interface ESIArbitrated loop physical address Alpa values SettingHex Dec TTL input characteristics provides the TTL characteristics Signal characteristicsDevice control codes FC Differential output LED driver signalsFC Differential input Receive eye diagram Eye diagram data values Link rate GHz Numerics IndexDevctrlcode FCP Mtbf Page See also cooling Page Cheetah 15K.7 FC Product Manual, Rev. C
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