Write Cache; Cache Operation - Fujitsu MJA2500BH - Mobile 500 GB Hard Drive Product/Maintenance Manual

Operations

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:
•
WRITE SECTOR(S) (EXT)
• WRITE MULTIPLE (EXT) (FUA)
• WRITE DMA (EXT) (FUA)
•
WRITE FP DMA QUEUED
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.
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 COMRESET, a software 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.
6-20 C141-E293