Seagate ST2000NM0063 manual Caching write data, Prefetch operation

Page 17

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 disk 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 capability 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.

4.5.1Caching 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 available 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 generated.

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 10 shows the mode default settings for the drive.

4.5.2Prefetch operation

If the Prefetch feature is enabled, data in contiguous logical blocks on the disk 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 disk 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.

CONSTELLATION ES.1 SAS PRODUCT MANUAL, REV. G

11

Page 16 Page 18
Image 17
Page 16 Page 18
Contents Constellation ES.1 SAS Document Revision History Contents Installation Inquiry data 11.3.2 Mode Sense data Figures Seagate Technology Support Services Model Number Self-Encrypting Drive SED Fips 140-2 Level ScopeApplicable Standards and Reference Documentation Taiwanese Bsmi Korean KCCEuropean Union Restriction of Hazardous Substances RoHS China Restriction of Hazardous Substances RoHS DirectiveSAS Interface Manual General Description Standard Features DDADF508 Read Write Average Single track Performance CharacteristicsFull stroke Maximum without verifyGeneral performance characteristics Prefetch operation Caching write dataRecoverable Errors Reliability SpecificationsUnrecoverable Errors Seek errorsHot plugging the drive Preventive maintenanceControlling S.M.A.R.T 4 S.M.A.R.TPerformance impact Reporting controlParameter Code Description Thermal monitorDrive Self Test DST DST failure definitionImplementation State of the drive prior to testingInvoking DST Short and extended testsAbort Product warrantyShipping StoragePHYSICAL/ELECTRICAL Specifications 0Gb mode Amps 2TB drive Standard & SED model DC power requirements1TB drive Standard & SED model DC power requirements 500GB drive Standard & SED model DC power requirements Current profiles Power sequencingConducted noise immunity TB model current profiles GB model current profiles Power Dissipation Constellation ES.1 SAS Product MANUAL, REV. G Constellation ES.1 SAS Product MANUAL, REV. G Constellation ES.1 SAS Product MANUAL, REV. G Constellation ES.1 SAS Product MANUAL, REV. G Constellation ES.1 SAS Product MANUAL, REV. G Relative humidity Temperature a. OperatingEffective altitude sea level a. Operating Shock and vibrationShock Package size Packaged/product weight Drop heightVibration Air cleanlinessAcoustics Corrosive environmentMounting configuration dimensions Weight maximumSeagate Enterprise SED PurposeValidation Program Default password Admin SPAbout SELF-ENCRYPTING Drives Locking SPSanitize Cryptographic Erase Drive Internal DEFECTS/ERRORS Defect and Error ManagementRead and write retry count maximum recovery times Identifying a Protection Information drive Setting and determining the current Type LevelLevels of PI Physical interface InstallationX = F 15lb = 67N Task management functions Interface RequirementsSAS task management functions supported Task management responsesCommand name Command code Supported Supported commandsSupported commands Supported commands Supported commands Inquiry data Mode Sense data Mode Pages Mode Sense data changeable and default values for 1TB drives Mode Pages Supported Feature or condition Miscellaneous featuresMiscellaneous status Supported StatusDatum B Section C C Section a a Connector requirements Physical characteristicsPin Signal name Signal type Electrical descriptionSAS transmitters and receivers PowerReady LED Out Ready LED Out conditionsGeneral interface characteristics LED drive signalDifferential signals Index Latency Index SAS Seagate Technology LLC

ST2000NM0063 specifications

The Seagate ST2000NM0063 is a high-performance internal hard disk drive designed for enterprise environments, offering a robust solution for those requiring reliable data storage. With a storage capacity of 2TB, this drive is ideal for both small and large enterprises, catering to applications ranging from data centers to surveillance systems.

One of the main features of the ST2000NM0063 is its 7200 RPM rotational speed, which ensures rapid data access and improved overall performance. This speed allows for faster read and write times, making it suitable for applications that demand quick data retrieval and processing. The drive supports a SATA 6Gb/s interface, which provides enhanced data transfer rates. This modern interface is essential for maximizing throughput, particularly when deployed in environments where speed is critical.

In terms of technology, the Seagate ST2000NM0063 utilizes Advanced Format Technology, enhancing data storage efficiency and increasing the number of user-addressable sectors. This feature allows for better alignment of data on the drive, which can lead to improved performance and reliability. Additionally, the drive incorporates the Seagate PowerChoice technology, enabling energy-efficient operations. This technology helps reduce power consumption during idle periods, contributing to lower operating costs and a smaller carbon footprint.

The ST2000NM0063 also emphasizes data integrity and reliability. Equipped with features such as error recovery control and vibration tolerance, this drive is designed to operate in challenging conditions. These attributes make it an excellent choice for RAID configurations and other enterprise applications that require high data availability and protection against data loss.

Furthermore, the ST2000NM0063 has a mean time between failures (MTBF) rating of 1.2 million hours, signifying its durability and long lifespan. This reliability is crucial for critical business applications where downtime is not an option.

In summary, the Seagate ST2000NM0063 combines high capacity, excellent performance, and advanced technologies to meet the demanding needs of enterprise storage. Its reliability, efficiency, and robust features make it a preferred choice for organizations looking to enhance their data storage solutions while ensuring optimal performance and longevity. Whether utilized in cloud storage, surveillance, or data center applications, this hard drive stands out as a dependable component in any IT infrastructure.
Top Page Image Contents