JPH11232037A - Magnetic disk device having disk cache write function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the decrease of frequency disabling write cache performance because of buffer empty wait and the improvement of performance through a method for temporarily and sequentially writing write data into a saving area provided on a disk corresponding to write commands continuously issued by random access. SOLUTION: The continuous write to positions 21, 22 and 23 on a recording medium is temporarily and sequentially performed into the saving area shown by 20. When there is no host access, the data written in the saving area are returned to the positions 21, 22 and 23. Since the write end of write data to the saving area corresponding to the write command continuously issued by the random access becomes the end of write to the host requested position, seeking from the position 21 to 22 and from 22 to 23 on the disk is not required and a buffer can be made empty speedily just for that time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention aims at shortening the write time on a disk and improving the performance of write commands continuously issued by random access.
Therefore, it is used for a magnetic disk device in which these accesses occur.

[0002]

2. Description of the Related Art In a magnetic disk device, a write command is completed when reception of write request data to a buffer in response to a write command is completed, and write performance is improved by using a write cache function of writing the data to a disk later. ing. The write cache functions in response to write commands that are continuously generated by sequential access or random access, and the processing becomes effective as the time until a buffer becomes available, that is, the time to write to the disk, becomes faster.

In the present invention, a save area provided on a disk is used to improve performance. JP-A-5-189863
In Japanese Patent Application Laid-Open Publication No. H10-209, if the power supply abnormality (short interruption) occurs before the data in the data buffer is written to the recording device, the data in the data buffer is saved in a save area provided on the disk. Has attempted to use the evacuation area. In addition, although the names are different, in Japanese Patent Application Laid-Open No. Hei 6-348597, a secondary cache area is provided on the disk to save data overflowing from the cache. When data overflows from the cache memory, the data is sequentially written to the secondary cache area, and the performance is improved by using the cache and the secondary cache.

[0004]

In a small disk device such as a 2.5-inch disk, the buffer capacity as a cache in the disk device is small, so the frequency with which the buffer becomes full depends on the type of the host, but is quite high. It is expected to be. When a write command is continuously issued by random access and the buffer in the disk device becomes full, the next write command cannot be received until the buffer becomes empty by writing on the disk. The time required for the buffer to become empty is longer than in sequential access because random access involves moving the head to the target position between commands.

The cache control disclosed in Japanese Patent Application Laid-Open No. 6-348597 is based on the case where a secondary cache is used to save data or the like which is determined to be most suitable for being evicted when the cache memory is full, or when a cache hit occurs in the secondary cache. Processing such as returning the data to the cache is performed. Since the data to be saved in the secondary cache overflows from the cache, there are probably various patterns. Therefore, the performance may be degraded depending on the save data. In the present invention, command processing using the save area is performed for a pattern that is considered to have the longest time until a buffer becomes available, that is, a write command that is continuously issued by random access.

According to the present invention, data is sequentially written to a save area only when a write command is continuously issued by random access, thereby reducing the overhead of moving a head to a target position and improving performance.

[0007]

In order to realize the present invention, a function for judging whether write commands are continuously issued by random access and write data in response to write commands continuously issued by random access are sequentially written on a disk. There is provided a function for writing, an area for temporarily saving the data on the disk, and a function for writing the saved data to the host request position when there is no access request from the host. Writing data to the host request position when there is no access request from the host has the effect of preventing the host from seeing the existence of the save area. Due to this effect, the host determines that the writing on the disk has been completed even though the writing has not been actually performed at the requested position, so that the next write command can be issued more quickly.

By applying the method proposed in the present invention to a magnetic disk drive, the frequency of losing the write cache function while waiting for a free buffer space is reduced, and the performance for write commands continuously issued by random access can be improved. Become.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a flowchart of an embodiment of the present invention. As a specific example of the present invention, it is assumed that write commands are continuously issued from the host, and description will be given based on FIG.

In judgment 1, the current command is compared with the previous command. Here, it is assumed that the write commands are issued successively, so that the determination 2 is performed next.

In determination 2, the cylinder, head, and sector at the end position of the previous write command and the start position of the current write command are compared to determine whether the access pattern is random. If the access is a random access, the current command is written into a save area provided on the disk at a position sequential with the previous command (process 3). At this time, the cylinder requested by the host,
Information such as a head, a sector, and the number of blocks is stored in a save area management table on the disk controller. The information stored in the table takes a format determined by information collected from a disk controller or the like, and is referred to later when reading data in the save area and when writing data at a position requested by the host.
After the data writing is completed, the pointer for indicating the start position of the save area is updated by processing 4. The write start position to the evacuation area is determined by this pointer,
The pointer always moves such that writing to the save area is sequential.

Next, a decision 5 is made to perform the operation of returning the data stored in the evacuation area to the original position. If the host is not being accessed, the data in the save area is read (process 6), and the pointer used in the save area is returned (process 7). The read data is written to the host request position calculated from the save area management table (process 8). Finally, it is determined whether data remains in the evacuation area (determination 9). If remaining, the processing of judgment 5 and thereafter is repeated.

FIG. 2 shows a visual representation of an embodiment of the present invention. The host issues a write command continuously to the positions 21, 22, and 23 on the recording medium. Since the positions 21, 22, and 23 have a random positional relationship, in a normal operation, head movement to each position and data writing are repeated. In the present invention, data is sequentially written in the save area indicated by the dotted line 20 in the format shown in the figure. Here, the pointer A indicates a write start position, and indicates a position where the write to the save area is always sequential. In the figure, the pointer A becomes the position 25 at the end of the writing to the first evacuation area (writing to the position 21). At the end of the next write (write to position 22), pointer A becomes position 26. At this point, when the data in the save area is returned to the position 22, the pointer A
Also returns to position 25.

The data written in the save area refers to the save area management table to determine the position on the recording medium, and when there is no host access, the host request position (21, 22,
23 position).

In the present invention, the end of writing to the save area has the same meaning as the end of writing to the host requested position. In the case of a random access write, the write operation on the disk is completed only after a seek operation to the target position is performed.
Movement of head from position to position 22 and position 23 from position 22
As the time required for moving the head to the buffer becomes empty, the buffer becomes empty, and the frequency at which the write cache does not function while waiting for an empty buffer is reduced.

[0016]

According to the present invention, the frequency at which the write cache does not function due to the buffer empty waiting is reduced by using the save area for write commands continuously issued by random access, and the performance is improved.

[Brief description of the drawings]

FIG. 1 is an example of a flowchart for realizing the present invention.

FIG. 2 is a visual diagram for explaining the present invention.

[Explanation of symbols]

1,2,5,9 ... decision branch, 3,4,6,7,8
... Execution processing, 20 ... Evacuation area, 21-
23: position on storage medium, 24-27: position of pointer.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Seiji Ono 2880 Kozu, Odawara-shi, Kanagawa Prefecture Hitachi, Ltd. Storage Systems Division

Claims (1)

[Claims] In response to a write command continuously issued by random access, a function of temporarily writing write data to a save area provided on a disk sequentially and having a function of writing data to a save area is provided. A magnetic disk drive having a function of writing to a host request position when there is no access request from the host.