Fujitsu MJA2500BH Maintenance Manual - Page 279

6.4 Read-ahead Cache 6.4.3.2 Sequential hit When the read command that is targeted at a sequential address is received after execution of the read commands is completed, the read command transmits the Read requested data to the host system continuing read-ahead without newly allocating the buffer for read. 1) When the sequential read command is received, HAP is set in the sequential address of the last read command, and DAP is set at a present read position as it is. HAP (host address pointer) Cache valid data Read requested data Read-ahead data Free space 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. HAP (host address pointer) Cache valid data Read requested data Free space DAP (disk address pointer) 3) When reading of read requested data is completed and transfer of the read requested data to the host system is completed, the read-ahead operation continues until a certain amount of data is stored. HAP (host address pointer) Cache valid data Read-ahead Free Read requested data data space DAP (disk address pointer) 4) The following cache valid data is for the read command that is executed next: Cache valid data LAST LBA START LBA C141-E293 6-17