6.5 Read-Ahead Cache

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

Cache data

Start LBA

Last LBA

6.5.3.4 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

 

 

 

 

Start LBA

Last LBA

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.

 

 

HAP

 

Requested data to be transferred

(stopped)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Partially hit data

Lack data

DAP (stopped)

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Fujitsu MHF2043AT, MHE2043AT, MHF2021AT, MHE2064AT manual Partially hit