Fujitsu MPA3035AT, MPA3043AT, MPA3052AT manual Read-Ahead Cache, 9 Data buffer configuration

(3)Automatic alternate assignment

The device performs the automatic assignment at following case.

1)When ECC correction performance is increased during read error retry, a read error is recovered.

Before automatic alternate assignment, the device performs rewriting the corrected data to the erred sector and rereading. If no error occurs at rereading, the automatic alternate assignment is not performed.

2)When a write error occurs and the error does not recovered.

6.5Read-Ahead Cache

After read command which involves 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.

6.5.1Data buffer configuration

The drive has a 128-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).

128 KB (131,072 bytes)

for read commands	for write commands	for MPU work
65,536 bytes (128 sectors)	48,640 bytes (95 sectors)	16,896 bytes

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.

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