Fujitsu MHV2080AS, MHV2060AS, MHV2040AS manual Using the read segment buffer, Miss-hit

6.4 Read-ahead Cache

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.)

HAP (host address pointer)

Read segment

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

Read requested data is stored until this point

Read requested data Free space

DAP

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.

HAP (stop)

Read requested data Read-ahead data

DAP

4) The following cache valid data is for the read command that is executed next:

Cache valid data

LAST LBA START LBA

C141-E221 6-15