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6.5 Read-Ahead Cache
C141-E050-02EN 6-21
3) The cache data for next read command is as follows.
Cache data
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.
Last LBA
Cache data
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
DAP
Partially hit data Lack data
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.
(stopped)
HAP
(stopped)
Requested data to be transferred
DAP
Partially hit data Lack data
Start LBA
Last LBA
Start LBA