Seagate ST373455LC manual Start/stop time, Prefetch/multi-segmented cache control, Cache operation

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5.3Start/stop time

After DC power at nominal voltage has been applied, the drive becomes ready within 20 seconds if the Motor Start Option is disabled (i.e., the motor starts as soon as the power has been applied). If a recoverable error condition is detected during the start sequence, the drive executes a recovery procedure which may cause the time to become ready to exceed 20 seconds. During spin up to ready time the drive responds to some com- mands over the SCSI interface in less than 3 seconds after application of power. Stop time is 30 seconds from removal of DC power.

If the Motor Start Option is enabled, the internal controller accepts the commands listed in the SCSI Interface Product Manual less than 3 seconds after DC power has been applied. After the Motor Start Command has been received the drive becomes ready for normal operations within 20 seconds typically (excluding an error recovery procedure). The Motor Start Command can also be used to command the drive to stop the spindle (see the SCSI Commands Reference Manual).

There is no power control switch on the drive.

5.4Prefetch/multi-segmented cache control

The drive provides prefetch (read look-ahead) and multi-segmented cache control algorithms that in many cases can enhance system performance. “Cache” as used herein refers to the drive buffer storage space when it is used in cache operations. To select prefetch and cache features the host sends the Mode Select command with the proper values in the applicable bytes in Mode Page 08h (see the SCSI Interface Product Manual). Prefetch and cache operation are independent features from the standpoint that each is enabled and disabled independently via the Mode Select command. However, in actual operation the prefetch feature overlaps cache operation somewhat as is noted in Section 5.5.1 and Section 5.5.2.

All default cache and prefetch Mode parameter values (Mode Page 08h) for standard OEM versions of this drive family are given in Table 10.

5.5Cache operation

Note. Refer to the SCSI Interface Manual for more detail concerning the cache bits.

Of the 16 Mbytes physical buffer space in the drive, approximately 13,000 kbytes can be used as a cache. The buffer is divided into logical segments from which data is read and to which data is written.

The drive keeps track of the logical block addresses of the data stored in each segment of the buffer. If the cache is enabled (see RCD bit in the SCSI Interface Manual), data requested by the host with a read com- mand is retrieved from the buffer, if possible, before any disc access is initiated. If cache operation is not enabled, the buffer is still used, but only as circular buffer segments during disc medium read operations (dis- regarding Prefetch operation for the moment). That is, the drive does not check in the buffer segments for the requested read data, but goes directly to the medium to retrieve it. The retrieved data merely passes through some buffer segment on the way to the host. All data transfers to the host are in accordance with buffer-full ratio rules. See the explanation provided with the information about Mode Page 02h (disconnect/reconnect control) in the SCSI Interface Manual.

The following is a simplified description of the prefetch/cache operation:

Case A—read command is received and all of the requested logical blocks are already in the cache: 1. Drive transfers the requested logical blocks to the initiator.

Case B—A Read command requests data, and at least one requested logical block is not in any segment of the cache:

1.The drive fetches the requested logical blocks from the disc and transfers them into a segment, and then from there to the host in accordance with the Mode Select Disconnect/Reconnect parameters, page 02h.

2.If the prefetch feature is enabled, refer to section 5.5.2 for operation from this point.

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Cheetah 15K.5 SCSI Product Manual, Rev. J

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Contents Cheetah 15K.5 Scsi Page Contents Defect and error management InstallationInterface requirements List of Figures Page Seagate Technology support services Seagate Online Support and ServicesScope Electromagnetic compatibility Applicable standards and reference documentationStandards Electromagnetic susceptibilityElectromagnetic compliance European Union Restriction of Hazardous Substances RoHSReference documents Drive model number vs. differentiating features General descriptionStandard features Media characteristicsPerformance ReliabilityFormatted capacities Accessories Factory installed accessoriesOptions factory installed Programmable drive capacityPerformance characteristics Internal drive characteristics transparent to userScsi performance characteristics visible to user Format command execution time minutes Generalized performance characteristicsSeek time Start/stop time Prefetch/multi-segmented cache controlCache operation Caching write data Prefetch operationRecoverable Errors Reliability specificationsError rates Unrecoverable ErrorReliability and service Seek errorsPreventive maintenance Hot plugging Cheetah 15K.5 Scsi disc drives 4 S.M.A.R.TMilliseconds Controlling S.M.A.R.TPerformance impact Reporting controlTemperature Log page 0Dh Parameter Code Description Thermal monitorDrive Self Test DST Implementation State of the drive prior to testingDST Failure Definition Invoking DSTExtended test Function Code 010b Product warrantyShort test Function Code 001b Log page entriesShipping Product repair and return informationDC power requirements Physical/electrical specificationsAC power requirements ST3300655LC DC power requirementsST3146855LC DC power requirements ST373455LC DC power requirementsPower sequencing Conducted noise immunityCurrent profile Typical ST3300655LW drive +12V LVD current profile Power dissipation ST3300655LW/ST3300655LCST3146855LC DC current and power vs. Iops LVD ST3146855LW/ST3146855LCST373455LC DC current and power vs. Iops LVD ST373455LW/ST373455LCRelative humidity Temperature a. OperatingEnvironmental limits Effective altitude sea level a. OperatingShock and vibration ShockRecommended mounting Air cleanliness Vibration a. Operating-normalCorrosive environment Mechanical specifications AcousticsLC mounting configuration dimensions Defect and error management Drive error recovery proceduresDrive internal defects Read and write retry count maximum recovery times Scsi systems errors Background Media ScanMedia Pre-Scan Deferred Auto-Reallocation Idle Read After WriteDrive ID/option select header InstallationConfigure drive options FormattingJ5 jumper header on LW models only Drive Front Function description RESDrive orientation CoolingDrive mounting GroundingScsi interface messages supported Interface requirementsGeneral description Scsi messages supported by Cheetah 15K.5 Scsi family drivesScsi interface commands supported Commands supported by Cheetah 15K.5 Scsi family driveCommands supported by Cheetah 15K.5 Scsi family drive Commands supported by Cheetah 15K.5 Scsi family drive Commands supported by Cheetah 15K.5 Scsi family drive Cheetah 15K.5 Scsi family drive Standard Inquiry data Inquiry Vital Product dataMode Sense data ST3300655 Mode sense data Mode Sense Pages DataST3146855 Mode sense data Mode Sense Header Data Mode Sense Pages DataST373455 Mode sense data Scsi bus conditions and miscellaneous features supported Scsi bus conditions and other miscellaneous featuresSynchronous data transfer Physical interfaceDC cable and connector Scsi interface physical description Scsi interface cable requirements Mating connectorsInterface transfer rates supported Cable requirementsMating connectors for LW model drives Mating connectors for LC model drivesRight-angle to Pcba connectors Scsi daisy-chain interface cabling for LW drivesNonshielded 68-pin Scsi device connector used on LW drives Nonshielded 80-pin Scsi SCA-2 connector used on LC drives GND LW 68-conductor LVD P cable signal/pin assignments LC 80-pin single-ended SE I/O connector pin assignments Active LED OUT 4LC 80-pin single-ended LVD I/O connector pin assignments +5 V Charge GND Active LED OUT 4LVD output characteristics Electrical descriptionMultimode-SE and LVD alternatives Cable characteristics for single-ended circuits LVD Input characteristicsGeneral cable characteristics Single-ended drivers/receiversCables for low voltage differential drivers/receivers Twist-n-flat cables-into a multi-drive backplaneTerminator requirements Terminator power LW drivesLC drives Disc drive Scsi timing Disc drive Scsi timingDisc drive Scsi timing Drive activity LED status Spindle status Command status Drive activity LEDSymbols NumericsPage Page Scsi Page Page