Datasheet

Data Buffer Management
3-2 C141-C008
Segment 7
Segment 6
Segment 5
Segment 4
←
Read
←
Read
Write
→
Segment 3
Segment 2
Segment 1
Segment 0
Valid Data
Write
→
Disk Media
INIT
Segment
Figure 3.1 Data buffer configuration (in the case of 8 cache segments)
The basic functions and operations of the data buffer in a read operation and a
write operation are shown below.
(1) Read operation
Data read from the disk media are temporarily stored in the data buffer.
Then, they are transferred to the FC interface with the timing specified in the
MODE SELECT parameter. The basic read operation procedure is as shown
below.
1) When the IDD receives a command, normally, it disconnects from the
FC interface through disconnect processing and locates the data block
specified by the command where it is stored on the disk media.
2) When the target data block has been located, the IDD reads the data form
the disk media to the data buffer. At this time, if a recoverable error is
detected, the IDD performs error recovery processing according to the
specification in the MODE SELECT parameter or corrects the data in the
data buffer.
3) When the IDD has read the amount of data specified by the buffer full
ratio in the MODE SELECT parameter (see Section 3.1.2) to the data
buffer, it performs reconnection processing with the FC interface and
begins transferring data to the INIT (FC interface) from the data buffer
while continuing to read subsequent data blocks to the data buffer.
4) If the data transfer capacity of the INIT (FC interface) is high and the
data buffer becomes empty before completing transfer of the number of
data blocks specified by the command, the IDD performs disconnect
processing at that point. Thereafter, Loop OPEN, data transfer and Loop
CLOSE (the operations in 3) and 4) above) are repeated until all the data
blocks specified in the command have been transferred.