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 avail- able 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 gen- erated.

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.

Tables 10, 11, and 12 shows the mode default settings for the drives.

4.5.2Prefetch operation

If the Prefetch feature is enabled, data in contiguous logical blocks on the disc 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 disc 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 ST373355SS, ST3146755SS, ST3300555SS manual Caching write data, Prefetch operation
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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.
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