Fujitsu MAT3300FC 사용자 설명서

C141-C008 

3-1 

3.1 Data 

Buffer 

3.2 

Look-Ahead Cache Feature 

3.3 Write 

Cache 

 

In this chapter, the configuration of the data buffer with which the IDD is 
equipped, its operation and the operation of the cache feature are described. 

The IDD is equipped with a 6,797 KB data buffer, which makes it possible to 
efficiently execute data transfer operations between INIT (initiator) and a disk 
drive. 

The IDD divides data buffer into 64 Pages, which are minimum allocation size for 
Cache. Actually two or more Pages are linked and a Cache Segment is 
constructed per the requested data size from INIT. 

Since IDD automatically controls the best suitable Cache Segment, INIT cannot 
be changed neither the Page size nor the Segment size. 

Each data buffer is a 2 ports of FIFO (First-In First-Out) ring buffer, with one port 
allocated for transfers with the disk media and the other port for data transfers 
with the FC interface.  Mutual ports operate asynchronously and since it is 
possible to efficiently absorb variations in data transfer speed between the ports, 
the INIT can perform data transfer operations with the IDD while being virtually 
unaware of differences between the FC interface data transfer rate and the disk 
drive data transfer rate. 

Even if the data transfer capacity of the FC interface (INIT) is lower than the disk 
drive's data transfer rate, the data buffer can perform data transfers to the system 
under optimum conditions without using sector interleave.  Also, if the data 
transfer capacity of the FC interface (INIT) is higher than the disk drive's data 
transfer rate, it is possible to minimize the occupancy time on the FC Loop by 
accumulating an appropriate amount of data in the data buffer. 

Only one cache segment of the divided data buffer is used by one command and 
the data in the other cache segments are held. 

Figure 3.1 shows the data buffer image.