Fujitsu MHS2020AT, Product Manual, Page: 233 / 254

6.4 Read-ahead Cache
C141-E171-03EN 6-15
6.4.3 Using the read segment buffer
Methods of using the read segment buffer are explained for the following
situations.
6.4.3.1 Miss-hit (no 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 point) and DAP (disk address point) are defined in the
sequential address of the segment that is read last.
Read segment
DAP (disk address pointer)
HAP (host 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
Read requested data is
stored until this point.
Free space
DAP
HAP
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
(stop)
HAP
(stop)