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6.5 Read-Ahead Cache
C141-E050-02EN 6-19
b. Sequential hit
When the previously executed read command is the sequential command
and the last sector address of the previous read command is sequential to
the lead sector address of the received read command, the disk drive
transfers the hit data in the buffer to the host system.
The disk drive performs the read-ahead operation of the new continuous
data to the empty area that becomes vacant by data transfer at the same
time as the disk drive starts transferring data to the host system.
1) In the case that the contents of buffer is as follows at receiving a read
command;
Start LBALast LBA
DAP
HAP (Continued from the previous read request data)
Hit dataRead-ahead data
2) The disk drive starts the read-ahead operation to the empty area that becomes
vacant by data transfer at the same time as the disk drive starts transferring hit
data.
DAP
HAP
Hit dataNew read-ahead dataRead-ahead data
3) After completion of data transfer of hit data, the disk drive performs the read-
ahead operation for the data area of which the disk drive transferred hit data.
Read-ahead data
HAP
DAP