Electrical computers and digital processing systems: memory – Storage accessing and control – Specific memory composition
Reexamination Certificate
1999-01-27
2001-08-07
Nguyen, Hiep T. (Department: 2187)
Electrical computers and digital processing systems: memory
Storage accessing and control
Specific memory composition
C710S056000
Reexamination Certificate
active
06272589
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to, for example, a hard disk drive, and more particularly to a disk controller for controlling write buffering.
A hard disk drive (HDD) is connected to a host system such as a computer system or the like and then used as a data storage device. The HDD receives data transferred from the host system and records the data (write data) on a disk, or data recording medium. The HDD reads data from the disk and transfers the data (read data) to the host system. The speed of data transfer between the host system and the HDD (host data transfer) is different from the speed of data transfer in the HDD, namely to and from the disk (disk data transfer). To compensate for the difference between these speeds, the HDD incorporates a buffer memory (RAM).
The buffer memory has a read buffer area and a write buffer area. The read buffer area is provided for temporarily storing data read from the disk. The write buffer areas is provided for temporarily storing data to be written on the disk. The ratio in size between the read and write buffer areas depends on the design specification of the buffer memory. In most cases, the read buffer area is larger than the write buffer area.
Upon receipt of a write command from the host system, the HDD receives write data transferred from the host system. In the HDD, the write data is temporarily stored in the write buffer area of the buffer memory. Meanwhile, the magnetic head for reading data on the disk and writing data therefrom is moved to prescribed position (a target access track) on the disk that is spinning at high speed. The magnetic head is thus prepared to write data on the disk. The write data is read from the write buffer area of the buffer memory, in units sectors. Then, the magnetic head writes data sequentially in those of the sectors provided on the disk which have been designated, first in the first of the designated sectors.
The speed of host data transfer depends on the performance (data-processing ability) of the host system. Hence, the speed of data transfer between one host system and an HDD differs from the speed of data transfer between another host system and an HDD of the same performance.
The speed of host data transfer may be higher than the speed of disk data transfer (i.e., the speed of recording data on the disk). In this case, data is written in the write buffer area faster than data is read from the read buffer area in the buffer memory. The write buffer area will become full more quickly than the read buffer area. Once the write buffer area becomes full, the HDD stops the host data transfer until the write buffer area becomes empty in part. The HDD starts the host data transfer again when some write data is read from the write buffer area, rendering the area partly empty.
Conversely, the speed of host data transfer may be lower than the speed of disk data transfer. If this is the case, the write buffer area of the buffer memory will become empty more quickly than the read buffer area. The write buffer area becomes empty when all write data is read from the buffer memory and written on the disk. Once the write buffer area becomes empty, the HDD starts waiting for any write data that will be transferred from the host system. As soon as write data (data for at least one sector of the disk) is transferred from the host system to the write buffer area, the HDD starts writing the data on the disk.
Recently it is observed that the drive data transfer is faster than the host data transfer in many cases because it takes much time to process write data in the host system and to transfer the data to the HDD. Hence, there is the trend that the write buffer area becomes empty more quickly than the read buffer area. When the write buffer area of the buffer memory becomes empty, the starts waiting for any write data that will be transferred from the host system. The moment write data is transferred from the host system to the write buffer area, the HDD starts writing the data on the disk.
When the HDD stops writing data on the disk, the head moves past the sector in which data is to be written. The HDD can no longer write data on the disk until the disk rotates further once to bring the sector to the head. It is desired that the HDD write data in the designated sector and some following sectors in the same track which has been designated. In other words, the HDD should write data in a plurality of consecutive sectors of a designated track for the time T (e.g., 15 ms) which the disk needs to rotate once.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is make a disk drive write data efficiently on a disk without waiting until the disk rotates once, by using a buffer memory having a write buffer area of an appropriate size, even if data is transferred between the disk drive and a host system at a relatively low speed. Another object of the invention is to prevent a buffer memory from having an empty part by minimizing the write buffer area of the buffer memory in accordance with the speed of transferring write data from a host system, thereby to enhance the use efficiency of the buffer memory.
In order to attain the objects the invention provides a disk drive having a disk on which write data transferred from a host system is recorded in accordance with a write command supplied from the host system. The disk drive comprises: a buffer storage having a write buffer area for temporarily storing the write data transferred from the host system; a disk controller for reading the write data from the write buffer area and writing the write data on the disk; monitoring means for monitoring a change in an amount of data accumulated in the write buffer area; and control means for changing the storage size of the write buffer area to a new storage size in accordance with the change monitored by the monitoring means.
The monitoring means monitors the change in the amount of data accumulated in the write data area. If the speed of host data transfer is low, the storage size of the write buffer area is changed, preventing the write buffer area from becoming empty. Since the write buffer area never becomes empty, the writing of the data onto the disk is not interrupted at all. In other words, the disk drive can write data efficiently on the disk, without waiting until the disk rotates once.
Moreover, a decrease in the amount of data accumulated in the write buffer area which may occur during the time the disk requires to rotate once can be predicted by monitoring the change in the amount of data. The storage size of the write buffer area can be changed to a minimum storage size which corresponds to the decrease predicted. This helps to use the buffer memory with the highest possible efficiency.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 5758191 (1998-05-01), Kasebayashi et al.
patent: 6101329 (2000-08-01), Graef
patent: 6105070 (2000-08-01), Gaylord
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patent: 8-212015 (1996-08-01), None
Kabushiki Kaisha Toshiba
Moazzami Nasser
Nguyen Hiep T.
Pillsbury & Winthrop LLP
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