Fujitsu MHS2020AT, Product Manual

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6.4 Read-ahead Cache
C141-E171-03EN 6-17
b. Sequential hit
When the end sector address of the read command received the last time and the
top sector address of the read command this time are consecutive, hit data already
stored on the buffer is transferred to the host system.
At the same time as a transfer of the hit data to the host system starts, the new
read-ahead operation for the subsequent data is implemented in the free space that
has been made available by the data transfer.
1) The following state is established when the read command is received.
START LBA LAST LBA
DAP
HAP (being consecutive after the last set of read requested data)
Hit data Read-ahead data
2) At the same time as a transfer of hit data starts, reading of read-ahead data is
started for as many spaces as are made available by the transfer.
DAP
HAP
Hit data New read-ahead data Read-ahead data
3) When transfer of the hit data is complete, the read-ahead operation is
performed as many times as required for the amount of transferred hit data.
Read-ahead data
HAP
DAP