Fujitsu MHU2100AT, Product Manual

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6.4 Read-ahead Cache
C141-E202-01EN 6-15
6.4.3 Using the read segment buffer
Methods of using the read segment buffer are explained for following situations.
6.4.3.1 Miss-hit
In this situations, the top block of read requested data is not stored at all in the
data buffer. As a result, all of the read requested data is read from disk media.
1) HAP (host address pointer) and DAP (disk address pointer) are defined in the
head of the segment allocated from Buffer. (If pre-read is executed, HAP is
set at the requested data reading position.)
Read segment
AP (host address pointer)
DAP (disk address pointer)
2) During reading of read requested data, the request data that has already been
read is sent to the host system.
Read requested data
Free space
HAP
DAP
Read requested data is
stored until this point
3) When reading of read requested data is completed and transfer of the read
requested data to the host system is completed, reading of the disk continues
until a certain amount of data is stored.
Read requested data Read-ahead data
DAP
HAP (stop)
4) The following cache valid data is for the read command that is executed next:
Cache valid data
START LBA LAST LBA