Fujitsu MHR2030AT User Manual download pdf (Page 228)

Operations

6-12 C141-E145-02EN

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 For R/W command

2048 KB (2097152 bytes)

80 KB

(81920 bytes)

1968 KB

(2015232 bytes)

Figure 6.7 Data buffer structure

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.

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Fujitsu MHR2030AT User Manual Page 228