6.5 Write Cache
6.5 Write Cache
Write Cache is the function for reducing the command processing time by separating command control to disk media from write control to disk media. When Write Cache is permitted, the write command can be keep receiving as long as the space available for data transfers remains free on the data buffer. Because of this function, command processing appears to be completed swiftly from the viewpoint of the host. It improves system throughput.
6.5.1 Cache operation
(1) Command that are targets of caching
The Commands that are targets of caching are as follows:
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WRITE SECTOR (S)
WRITE MULTIPLE
WRITE DMA
WRITE SECTOR (S) EXT
WRITE MULTIPLE EXT
WRITE DMA EXT
However, the caching operation is not performed when the caching function is prohibited by the SET FEATURES command.
(2) Invalidation of cached data
If an error occurs during writing onto media, write processing is repeated up to as many times as specified for retry processing. If retry fails for a sector because the retry limit is reached, automatic alternate sector processing is executed for the sector. If the automatic alternate sector processing fails, the data in the sector for which automatic alternate sector processing failed is invalidated without being guaranteed.
If data remains in sectors following a sector for which automatic alternate sector processing failed, the data is invalidated without being guaranteed.
Moreover, when the command (clause 6.4.2(3)) is accepted and HOST CRC Error is generated, the cashing data is invalidated.
<Exception>
•If a Reset or command is received while a transfer of one sector of data is in progress, data is not written in the sector of the media where the interruption occurred, and sectors accepted before interruption occurred is written in the medium.
