Seagate ST3300555SS, ST3146755SS manual Prefetch/multi-segmented cache control, Cache operation

Page 19

The START STOP UNIT command may be used to command the drive to stop the spindle. Stop time is 30 sec- onds (maximum) from removal of DC power. There is no power control switch on the drive.

4.4Prefetch/multi-segmented cache control

The drive provides a prefetch (read look-ahead) and multi-segmented cache control algorithms that in many cases can enhance system performance. Cache refers to the drive buffer storage space when it is used in cache operations. To select this feature, the host sends the Mode Select command with the proper values in 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 Section 9.3.2.

4.5Cache operation

Note. Refer to the SAS 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 SAS 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 (disregarding 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 SAS 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 4.5.2 for operation from this point.

Each cache segment is actually a self-contained circular buffer whose length is an integer number of logical blocks. The drive dynamically creates and removes segments based on the workload. The wrap-around capa- bility of the individual segments greatly enhances the cache’s overall performance.

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 T10 SAS Product Manual, Rev. A

13

Page 18 Page 20
Image 19
Page 18 Page 20
Contents Cheetah T10 SAS Page Contents Interface requirements Defect and error managementInstallation Seagate Technology support servicesList of Figures Cheetah T10 SAS Product Manual, Rev. a Cheetah T10 SAS disc drive ScopeCheetah T10 SAS Product Manual, Rev. a Electromagnetic susceptibility Standards, compliance and reference documentsStandards Electromagnetic compatibilityCompliance Reference documents Cheetah T10 SAS Product Manual, Rev. a General description Media description Standard featuresPerformance Programmable drive capacity Factory-installed accessoriesReliability Formatted capacitiesUser-installed accessories Options factory installedSeek time Performance characteristicsInternal drive characteristics Access timeGeneral performance characteristics Format command execution time minutesStart/stop time Cache operation Prefetch/multi-segmented cache controlPrefetch operation Caching write dataUnrecoverable Errors Reliability specificationsError rates Recoverable ErrorsPreventive maintenance Reliability and serviceSeek errors Interface errorsPerformance impact Hot plugging the drive4 S.M.A.R.T Controlling S.M.A.R.TThermal monitor Reporting controlDetermining rate Predictive failuresParameter Code Description Temperature Log Page 0DhPrimary Temperature Reference TemperatureShort test Function Code 001b State of the drive prior to testingInvoking DST Short and extended testsProduct repair and return information Product warrantyAbort ShippingCheetah T10 SAS Product Manual, Rev. a ST3300555SS DC power requirements Physical/electrical specificationsAC power requirements DC power requirementsST373355SS Gbit mode Amps ST3146755SS DC power requirementsST373355SS DC power requirements ST3146755SS Gbit mode AmpsCurrent profiles General DC power requirement notesPower sequencing Conducted noise immunityTypical ST3300555SS drive current profiles Typical ST3146755SS drive current profiles Typical ST373355SS drive current profiles ST3300555SS in 3 Gbit operation Power dissipationST3300555SS in 1.5 Gbit operation ST3146755SS in 1.5 Gbit operation ST3146755SS in 3 Gbit operationST373355SS in 1.5 Gbit operation ST373355SS in 3 Gbit operationEnvironmental limits Temperature a. OperatingShock Relative humidityEffective altitude sea level a. Operating Shock and vibrationRecommended mounting Package size Packaged/product weight Drop heightVibration a. Operating-normal Air cleanlinessCorrosive environment Acoustics Mechanical specificationsDrive internal defects/errors Defect and error managementDrive error recovery procedures Write retry count LBA cumulative, msec Background Media Scan SAS system errorsMedia Pre-Scan Idle Read After Write Deferred Auto-ReallocationDrive orientation InstallationAir flow CoolingGrounding Drive mountingCheetah T10 SAS Product Manual, Rev. a Interface requirements SAS featuresDual port support Commands supported by Cheetah T10 SAS family drives Scsi commands supportedCommand name Command code Supported Commands supported by Cheetah T10 SAS family drives Commands supported by Cheetah T10 SAS family drives Commands supported by Cheetah T10 SAS family drives Bytes Data hex Mode Sense dataInquiry data Cheetah T10 SAS inquiry dataPage Mode Pages ST3300555SS Mode Sense dataST3146755SS Mode Sense data ST373355SS Mode Sense data Miscellaneous status Miscellaneous operating features and conditionsMiscellaneous features Supported Feature or conditionSAS physical interface Datum B Connector requirements Physical characteristicsSAS pin descriptions Pin Signal name Signal typeElectrical description Pin descriptionsReady LED Out Signal characteristicsPower SAS transmitters and receiversEye masks Eye masks overview LED drive signalDifferential signals General interface characteristicsNormalized time in UI Receive eye maskJitter tolerance masks Absolute amplitudeFrequency in kHz Peak-toSinusoidal JitterSignal characteristica Units Gbps Transmitter signal characteristicsGbps m, n Deterministic jitterq Receiver signal characteristicsSignal characteristic Units Gbps Maximum allowable jitterImpedance requirements Sheet 1 Impedance specificationsReceiver jitter tolerance Compliant jitter test pattern CjtpatImpedance requirements Sheet 2 Transmitter characteristicsElectrical TxRx connections = -5,437dB Shows the zero-length test load Receiver characteristics Cheetah T10 SAS Product Manual, Rev. a Presales Support Seagate Technology support servicesWarranty Service Internet MySeagate Spp.seagate.comData Recovery Services Data Recovery Services Authorized Service CentersCall center Presales and Technical Support Warranty Service FAX services-All Europe toll callToll-free support numbers Africa/Middle East support services Numerics IndexPage SAS See also cooling Page Seagate Technology LLC

ST3300555SS, ST3146755SS, ST373355SS specifications

The Seagate ST373355SS, ST3146755SS, and ST3300555SS represent a range of high-performance hard drives designed for enterprise applications, particularly in server environments requiring reliability, speed, and high capacity.

The ST373355SS is a 73.5 GB SCSI hard drive operating at 15,000 RPM, which ensures rapid data access and superior performance, making it ideal for transactional applications and data-intensive tasks. With its 4 MB cache, the drive leverages fast read and write speeds, enhancing overall system responsiveness. The SCSI interface, operating at 80 MB/s, allows for high-speed data transfers, making it a suitable choice for demanding environments where quick access to information is critical. Its hot-swappable feature enables maintenance without shutting down the system, maximizing uptime and productivity.

The ST3146755SS, with a capacity of 146.8 GB, builds on the performance of its predecessor while introducing improvements in data handling and reliability. Operating at the same impressive 15,000 RPM, this model also features a 16 MB cache that greatly improves data throughput and access speed. The drive is designed to reduce latency, which is crucial for applications where timing is everything. It is equipped with advanced error recovery features and Seagate’s innovative PowerTrim technology, which improves power efficiency during read and write operations. The ST3146755SS also features a higher mean time between failures (MTBF), underscoring its reliability in high-demand environments.

Lastly, the ST3300555SS offers even greater capacity with 300 GB. This drive maintains the 15,000 RPM rotation speed and benefits from a 16 MB cache, providing a balance of speed and storage capacity. Its advanced SCSI interface supports not just speed but also data integrity, ensuring consistent performance during extensive data transfers. The drive is designed to handle workloads naturally associated with enterprise servers, data warehouses, and video editing applications. Its rugged build supports continuous operation and is tested for high-temperature environments to ensure durability.

In summary, the Seagate ST373355SS, ST3146755SS, and ST3300555SS hard drives are engineered for enterprise environments, combining impressive RPM speeds, significant storage capacities, and advanced technologies to deliver reliability, performance, and efficiency for critical applications. These hard drives represent Seagate's commitment to providing solutions that meet the rigorous demands of modern data environments.
Top Page Image Contents