Seagate ST373554FC, ST3146954FC, ST336854FC manual Cache operation

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4.5Cache operation

the applicable bytes in page 08h. Prefetch and cache operations are independent features from the standpoint that each is enabled and disabled independently using the Mode Select command; however, in actual opera- tion, the prefetch feature overlaps cache operation somewhat as described in sections 4.5.1 and 4.5.2.

All default cache and prefetch mode parameter values (Mode Page 08h) for standard OEM versions of this drive family are given in Table 18.

4.5Cache operation

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

Of the 16,384 kbytes physical buffer space in the drive, approximately 14,218 kbytes can be used as a cache. Cache segmenting is adjusted dynamically by the disk drive hardware according to the workload being experi- enced by the drive. The drive is capable of dynamically-adjusting up to 256 segments. The number and sizes of segments are not user-defined.

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 Fibre Channel Interface Manual), data requested by the host with a read command 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. On a cache miss, all data transfers to the host are in accordance with buffer-full ratio rules. On a cache hit, the drive ignores the buffer-full ratio rules. See the explanation pro- vided with the information about Mode Page 02h (disconnect/reconnect control) in the Fibre Channel Interface Manual.

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

Case A—read command is received and the first logical block is already in the cache:

1.Drive transfers to the initiator the first logical block requested plus all subsequent contiguous logical blocks that are already in the cache. This data may be in multiple segments.

2.When a requested logical block is reached that is not in any cache segment, the drive fetches it and any remaining requested logical block addresses from the disc and puts them in a segment of the cache. The drive transfers the remaining requested logical blocks from the cache to the host in accordance with the Mode Select Disconnect/Reconnect parameters, page 02h.

3.If the prefetch feature is enabled, refer to section 4.5.2 for operation from this point.

Case B—A Read command requests data, and the first 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 4.5.2 for operation from this point.

During a prefetch, the drive crosses a cylinder boundary to fetch data only if the Discontinuity (DISC) bit is set to 1 in bit 4 of byte 2 of the Mode Select parameters page 08h. Default is zero for bit 4.

Each cache segment is actually a self-contained circular buffer whose length is an integer number of logical blocks. The sizes of the segments are determined by the drive’s analysis of the current workload.

Note. The size of each segment is not reported by Mode Sense command page 08h, bytes 14 and 15. The value 0XFFFF is always reported regardless of the actual size of the segment. Sending a size specification using the Mode Select command (bytes 14 and 15) does not set up a new segment size. If the STRICT bit in Mode page 00h (byte 2, bit 1) is set to one, the drive responds as it does for any attempt to change an unchangeable parameter.

Cheetah 15K.4 FC Product Manual, Rev. B

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Contents ST3146954FC ST373554FC ST336854FC Cheetah 15K.4 FCPage ST3146954FC ST373554FC ST336854FC March Rev. A Revision status summary sheet07/15/05 Rev. B DraftPage 4.0 Performance characteristics Contents5.0 Reliability specifications 6.0 Physical/electrical specifications8.0 Installation 7.0 Defect and error management9.0 Interface requirements 10.0 Seagate Technology support services Cheetah 15K.4 FC Product Manual, Rev. B List of Figures Page Figure 1. Cheetah 15K.4 FC family disc drive 1.0 ScopeCheetah 15K.4 FC Product Manual, Rev. B 2.1 Standards 2.0 Applicable standards and reference documentation2.1.1 Electromagnetic compatibility 2.1.1.1 Electromagnetic susceptibilityElectromagnetic compliance for the European Union 2.1.2 Electromagnetic complianceAustralian C-Tick Korean MIC2.2 Reference documents Specification for Acoustic Test Requirement and ProceduresFibre Channel Interface Manual Cheetah 15K.4 FC Product Manual, Rev. B 3.0 General description 3.2 Media description 3.1 Standard features3.4 Reliability 3.3 Performance3.5 Formatted capacities 3.5.1 Programmable drive capacity3.7 Factory-installed options 3.6 Factory-installed accessories3.8 User-installed accessories 4.1 Internal drive characteristics 4.0 Performance characteristics4.2 Seek performance characteristics 4.2.1 Access timeGeneral performance characteristics 4.2.2 Format command execution time minutes4.3 Start/stop time 4.4 Prefetch/multi-segmented cache control4.5 Cache operation 4.5.2 Prefetch operation 4.5.1 Caching write dataCheetah 15K.4 FC Product Manual, Rev. B Cheetah 15K.4 FC Product Manual, Rev. B 5.1 Error rates 5.0 Reliability specifications5.1.1 Recoverable Errors 5.1.2 Unrecoverable Errors5.1.3 Seek errors 5.2 Reliability and service5.1.4 Interface errors 5.2.2 Preventive maintenance5.2.4 S.M.A.R.T 5.2.3 Hot plugging the driveControlling S.M.A.R.T Performance impact Fully-enabled delayMaximum processing delay On-line only delayDescription Parameter Code5.2.6 Drive Self Test DST 5.2.6.1 DST failure definition5.2.6.2 Implementation 5.2.6.2.1 State of the drive prior to testing5.2.6.2.2 Invoking DST 5.2.6.2.3 Short and extended tests5.2.6.2.4 Log page entries 5.2.7 Product warranty5.2.6.2.5 Abort ShippingProduct repair and return information 6.1 AC power requirements 6.0 Physical/electrical specifications6.2 DC power requirements 3 See +12V current profile in Figure 6.2.2 Power sequencing General DC power requirement notes6.2.1 Conducted noise immunity 6.2.3 Current profilesFigure 3. Typical ST3146954FC drive, 2 Gbit, +5V current profile Figure 2. Typical ST3146954FC drive, 2 Gbit, +12V current profileFigure 5. Typical ST373554FC drive +5V current profile Figure 4. Typical ST373554FC drive +12V current profileFigure 7. Typical ST336854FC drive +5V current profile Figure 6. Typical ST336854FC drive +12V current profileST3146954FC 6.3 Power dissipationPower watts ST373554FCST336854FC 6.4.1 Temperature a. Operating 6.4 Environmental limits6.4.2 Relative humidity 6.4.4 Shock and vibration 6.4.3 Effective altitude sea level a. Operating6.4.4.1 Shock Package size Packaged/product weightDrop height Figure 12. Recommended mounting6.4.4.2 Vibration a. Operating-normal 6.4.5 Air cleanliness6.4.6 Acoustics 6.4.7 Electromagnetic susceptibilityFigure 13. Mounting configuration dimensions 6.5 Mechanical specifications7.1 Drive internal defects/errors 7.0 Defect and error management7.2 Drive error recovery procedures Cheetah 15K.4 FC Product Manual, Rev. B 7.3 FC-AL system errors 7.4.1 Media Pre-Scan 7.4 Background Media Scan8.1 Drive ID/option selection 8.0 InstallationFigure 15. LED indicator connector 8.2 LED connectionsFigure 14. Physical interface 8.3 Drive orientation 8.2.1 J6 connector requirements8.4 Cooling 8.6 Grounding 8.5 Drive mountingK x X = F 15lb = 67N 9.1.1 Fibre Channel link service frames 9.1 FC-AL features9.0 Interface requirements 9.1.3 Fibre Channel task management responses 9.1.2 Fibre Channel task management functionsFibre Channel SCSI FCP task management functions Task nameNPort login PLOGI payload 9.1.4 Fibre Channel port loginBytes 9.1.6 Fibre Channel Process Login 9.1.5 Fibre Channel port login acceptNPort Login Accept ACC payload Process Login PLRI payload9.1.8 Fibre Channel fabric login 9.1.7 Fibre Channel Process Login AcceptProcess Login Accept ACC payload Fabric Login FLOGI payloadFabric Login Accept ACC payload 9.1.9 Fibre Channel fabric accept login9.1.10 Fibre Channel Arbitrated Loop options 9.2 Dual port supportTable 16 Supported commands 9.3 SCSI commands supportedCommand code Command nameTable 16 Supported commands continued Command code 3 Reference Mode Sense command 1Ah for mode pages supported 9.3.2 Mode Sense data 9.3.1 Inquiry data3. Current values CHG = Changeable bits indicates if default value is changeable4. Changeable values Definitions SAV = Current saved valueMODE SENSE 10 BYTE HEADER DATA Cheetah 15K.4 FC Product Manual, Rev. B Cheetah 15K.4 FC Product Manual, Rev. B Miscellaneous features 9.4 Miscellaneous operating features and conditionsFeature or condition Miscellaneous status9.5 FC-AL physical interface 9.5.1 Physical characteristics9.5.1.1 Physical description Features 9.5.2 Connector requirementsFC-AL SCA device connector dimensions Figure 20. J6 connector dimensions9.5.4 Pin descriptions 9.5.3 Electrical description9.5.7 Fault LED Out 9.5.6 Power9.5.5 FC-AL transmitters and receivers Figure 21. FC-AL transmitters and receivers9.5.8 Active LED Out 9.5.9 Enable port bypass signals9.5.10 Motor start controls Normal command activity9.5.11 SEL6 through SEL0 ID lines 9.5.11.1 Parallel Enclosure Services Interface ESIArbitrated loop physical address ALPA values SettingALPA SEL IDTTL input characteristics 9.6 Signal characteristics9.5.12 Device control codes 9.6.19.6.3 FC Differential output 9.6.2 LED driver signals9.6.4 FC Differential input Bit Time Vout mv XMIT EyeEye diagram data values Receive eye diagramVin mv 941 ps 659 ps 376 psCheetah 15K.4 FC Product Manual, Rev. B Online services 10.0 Seagate Technology support servicesSeagate Service Centers InternetUSA/Canada/Latin America support services Seagate Service Centers Customer Service OperationsWarranty Service Data Recovery ServicesAfrica/Middle East support services European support servicesFAX services-All Europe toll call Warranty ServiceAsia/Pacific support services Numerics IndexDownload microcode with offsets and save mode 7 front panel 38 FS 49, 50, 52 function NN 49 mounting 46 holes 46 orientationspin descriptions 66 PN 49 Self-Monitoring Analysis and Reporting Technology 9 LED driver 72 single-unit shipping pack kit 10 SMART 9 SMP = 1 in Mode Select command 63 SO 49UI 50, 51 unformatted Page Seagate Technology LLC