Fujitsu MBA3147RC, MBC2036RC, MBC2073RC, MBA3300RC, MBA3073RC Data Buffer, Write operation

3.1 Data Buffer

5)If the number of blocks specified in the command to be transferred is larger than the capacity of a cache segment and if the data transfer speed of the INIT is lower than the data transfer speed of the disk drive, the empty space in the data buffer disappears from step 3) and the HDD may soon not be able to read data from the disk media (data overrun). In this case, the HDD relocates the block that caused the data overrun after waiting one disk revolution, and continues the reading process.

When transfer of all the specified data is completed, the HDD reports the status and terminates the command.

(2) Write operation

After data transferred from the INIT are stored temporarily in the data buffer, they are written to the disk media. The basic write operation procedure is as shown below.

1)When the HDD receives a command, it transfers the XFER_RDY flame to INIT. Later it stores data transferred from the INIT to the data buffer (data pre-fetch). At this time, the HDD locates the position of the data block on the disk media specified by the command in parallel.

When storing of all the size of data specified in the XFER_RDY flame in the data buffer is completed, the HDD performs CLOSE processing.

2)When locating of the target data block on the disk media is completed, the HDD writes the data in the data buffer to the disk media. If the target data block location operation is completed during the data pre-fetch processing in 1), writing of data to the disk media is performed in parallel with the data pre- fetch to the data buffer.

3)If the data transfer speed of the INIT is lower than the data transfer speed of the disk drive, since the data pre-fetch of data that are to be written to that data block is not completed, it may not be possible to write the data continuously to the disk (data underrun). In this case, the HDD waits one disk revolution while continuing to pre-fetch data from the INIT, then repositions the block that caused the data underrun and continues the writing of data to the disk.

4)If all the blocks of data specified in the command have not yet been transferred from the INIT, as writing of data to the disk media progresses, at the point when the empty space in the data buffer reaches the amount specified by the HDD, the HDD performs OPEN processing and begins transferring the succeeding data (data pre-fetch) after it transfers the XFER_RDY frame.

Writing of data to the disk media is performed in parallel and data transfer with the INIT continues until the empty space in the data buffer is full or until transfer of all the data specified in the command is completed. From then on, the XFER_RDY data receiving are repeated until transfer of all the blocks of data specified in the command is completed.

5)When writing of all the specified data is completed, the HDD reports the status and terminates the command.

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