Seagate ST3300657SS Cheetah 15K.7 FC Product Manual - Page 18

Prefetch operation

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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 18 shows the mode default settings for the drive. 4.5.2 Prefetch 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. 12 Cheetah 15K.7 FC Product Manual, Rev. B

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12
Cheetah 15K.7 FC Product Manual, Rev. B
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 18 shows the mode default settings for the drive.
4.5.2
Prefetch 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 buf-
fer 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.