Read-Ahead Cache; Data Buffer Structure; Caching Operation; Figure 6.7 Data Buffer Structure - Fujitsu MHR2010AT Product Manual

Operations

6.4 Read-ahead Cache

Read-ahead Cache is the function for automatically reading data blocks upon
completion of the read command in order to read data from disk media and save
data block on a data buffer.
If a subsequent command requests reading of the read-ahead data, data on the data
buffer can be transferred without accessing the disk media. As the result, faster
data access becomes possible for the host.

6.4.1 Data buffer structure

This device contains a data buffer of 2 MB. This buffer is divided into two areas:
one area is used for MPU work, and the other is used as a read cache for another
command. (See Figure 6.7.)
For MPU work
80 KB
(81920 bytes)
The read-ahead operation is performed while the READ SECTOR (S) or READ
MULTIPLE or READ DMA command is in progress. Read-ahead data is stored
in the read cache part of the buffer.

6.4.2 Caching operation

The caching operation is performed only when the commands listed below are
received. If any of the following data are stored on the data buffer, the data is
sent to the host system.
All of the sector data that this command processes.
A part of the sector data including the start sector, that this command
processes.
If part of the data to be processed is stored on the data buffer, the remaining data
is read from disk media and sent to the host system.
6-12
2048 KB (2097152 bytes)
For R/W command
1968 KB
(2015232 bytes)

Figure 6.7 Data buffer structure

C141-E145-02EN