Fujitsu MHJ2181AT, MHK2120AT manual Read-Ahead Cache, Data buffer configuration, Caching operation

Operations

An unrecoverable write error occurs during write error retry, automatic alternate assignment is performed.

6.5 Read-Ahead Cache

After read command which involes read data from the disk medium is completed, the read-ahead cache function reads the subsequent data blocks automatically and stores the data to the data buffer.

When the next command requests to read the read-ahead data, the data can be transferred from the data buffer without accessing the disk medium. The host can thus access data at higher speed.

6.5.1 Data buffer configuration

The drive has a 512-KB data buffer. The buffer is used by divided into three parts; for read commands, for write commands, and for MPU work (see Figure 6.9).

512 MB (524,288 bytes)

for read commands for write commands for MPU work

262,144 byte (512 sector) 131,072 byte (256 sector)131,072 byte

Figure 6.9 Data buffer configuration

The read-ahead operation is performed at execution of the READ SECTOR(S), READ MULTIPLE, or READ DMA command, and read-ahead data is stored in the buffer for read commands.

6.5.2 Caching operation

Caching operation is performed only at issurance of the following commands. The device transfers data from the data buffer to the host system at issurance of following command if following data exist in the data buffer.

∙

∙

All sectors to be processed by the command

A part of data including load sector to be processed by the command

When a part of data to be processed exist in the data buffer, remaining data are read from the medium and are transferred to the host system.

(1) Commands that are object of caching operation

Follow commands are object of caching operation.

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