Fujitsu MHV2040BH, Руководство по эксплуатации продукта

Страница: 253 / 276

6.4 Read-ahead Cache
C141-E224 6-17
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.
Read-ahead data
Cache valid data Free space
Read requested data
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.
Cache valid data Free space Read requested data
DAP (disk address pointer)
HAP (host 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.
Read-ahead
data
Cache valid data
Free
space
Read requested data
DAP (disk address pointer)
HAP (host address pointer)
Read-ahead
data
4) The following cache valid data is for the read command that is executed next:
Cache valid data
START LBA LAST LBA
6.4.3.3 Full hit
In this situation, all read requested data is stored in the data buffer. Transfer of
the read requested data is started from the location where hit data is stored. For