Fujitsu MHA2021AT, MHA2032AT manual Last LBA

6.5 Read-Ahead Cache

(4) Partially hit

A part of requested data including a lead sector are stored in the data buffer. The disk drive starts the data transfer from the address of the hit data corresponding to the lead sector of the requested data, and reads remaining requested data from the disk media directly. The disk drive does not perform the read-ahead operation after data transfer.

Following is an example of partially hit to the cache data.

Cache data

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1)The disk drive sets the HAP to the address where the partially hit data is stored, and sets the DAP to the address just after the partially hit data.

HAP

Partially hit data

Lack data

DAP

2)The disk drive starts transferring partially hit data and reads lack data from the disk media at the same time. However, the disk drive does not perform the read-ahead operation newly.

Requested data to be transferred

HAP (stopped)

Partially hit data

Lack data

DAP

(stopped)

3)The cache data for next read command is as follows.

Cache data

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C141-E042-01EN 6-21