6.4 Read-Ahead Cache
1)
2)Data transferred to the host system once by requesting with the command that are object of caching operation (except for the cache invalid data by some reasons).
3)Remaining data in the data buffer (for write command) transferred from the host system by the command that writes data onto the disk medium, such as the WRITE SECTOR (S), WRITE DMA, WRITE MULTIPLE.
Followings are definition of in case that the write data is treated as a cache data. However, since the hit check at issuance of read command is performed to the data buffer for read command preferentially, caching write data is limited to the case that the hit check is missed at the data buffer for read command.
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When all data requested by the read command are stored in the data buffer for write command (hit all), the device transfers data from the data buffer for write command. At this time, the
Even if a part of data requested by the read command are stored in the data buffer for write command (hit partially), all data are read from the disk medium without transferring from the data buffer for write command.
(3) Invalidating caching data
Caching data in the data buffer is invalidated in the following case.
1)Following command is issued to the same data block as caching data.
−WRITE SECTOR(S)
−WRITE DMA
−WRITE MULTIPLE
2)Command other than following commands is issued (all caching data are invalidated)
−READ SECTOR (S)
−READ DMA
−READ MULTIPLE
−WRITE SECTOR(S)
−WRITE MULTIPLE
−WRITE VERIFY SECTOR(S)
3)Caching operation is inhibited by the SET FEATURES command.
4)Issued command is terminated with an error.
5)Soft reset or hard reset occurs, or power is turned off.
