Fujitsu MHR2010AT, Product Manual

Page: 229 / 250

6.4 Read-ahead Cache
C141-E145-02EN 6-13
(1) Commands that are targets of caching
The commands that are targets of caching are as follows:
•
READ SECTOR(S (EXT)
•
READ MULTIPLE (EXT)
•
READ DMA (EXT)
However, if the caching function is prohibited by the SET FEATURES command,
the caching operation is not performed.
(2) Data that is a target of caching
The data that is a target of caching are as follows:
1) Read-ahead data that is read from disk media and saved to the data buffer
upon completion of execution of a command that is a target of caching.
2) Data required by a command that is a target of caching and has been sent to
the host system once. If the sector data requested by the host has not been
completely stored in the read cache portion of the buffer, this data does not
become a target of caching. Also, if sequential hits occur continuously, the
caching-target data required by the host becomes invalid.
(3) Invalidating caching-target data
Data that is a target of caching on the data buffer is invalidated under the
following conditions:
1) Any command other than the following commands is issued. (All caching-
target data is invalidated.)
−
READ SECTOR(S)
−
READ MULTIPLE
−
READ DMA
−
CHECK POWER MODE
−
WRITE SECTOR (S)
−
WRITE MULTIPLE
−
WRITE DMA
2) The caching operation is invalidated by the SET FEATURES command.
3) Commands are issued with errors from the host side.
4) A soft/hard reset is issued or the power is turned off.