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 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 8 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 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.

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Seagate ST33000652SS, ST33000650SS, ST33000651SS manual Caching write data, Prefetch operation
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ST33000652SS, ST33000650SS, ST33000651SS specifications

The Seagate ST33000651SS, ST33000650SS, and ST33000652SS are high-performance enterprise hard drives designed for demanding storage applications. These models are part of the Seagate Constellation ES series, known for their reliability and performance in server and data center environments.

One of the most notable features of these drives is their capacity. The ST33000651SS and ST33000650SS offer a storage capacity of 3TB, providing ample space for data-intensive applications. The ST33000652SS enhances this with a larger storage option, ensuring that organizations can meet growing data demands without needing frequent upgrades.

These drives utilize a SATA 6Gb/s interface, which allows for high-speed data transfer. This increased bandwidth is essential for applications that rely on rapid access, such as virtualization, cloud computing, and database management systems. Additionally, the drives support Native Command Queuing (NCQ), which enhances performance by optimizing the order in which read and write commands are executed.

Reliability is paramount in enterprise environments, and Seagate addresses this with several technologies designed to minimize downtime. The ST33000651SS and its counterparts feature a 7200 RPM spindle speed, which not only delivers fast access times but also contributes to the overall durability of the drives. They also come with advanced error correction and data integrity features, which safeguard against data loss.

Another important characteristic of these drives is their low power consumption. Operating at an average power usage of 6.0W, they help reduce operational costs, particularly in large-scale deployments. This energy efficiency is essential for organizations looking to maintain sustainability while maximizing performance.

In terms of physical design, these hard drives are built to endure tough conditions typically found in data centers. They come in a standard 3.5-inch form factor, ensuring compatibility with a wide range of servers and storage enclosures. The robust design further enhances their lifespan, making them a sound investment for enterprise storage solutions.

In summary, the Seagate ST33000651SS, ST33000650SS, and ST33000652SS hard drives offer a compelling combination of high capacity, fast data transfer rates, and reliability. Their advanced technologies and energy-efficient design make them ideal choices for enterprises that require dependable and high-performing storage solutions in their IT infrastructure.
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