JP2914834B2 - Magnetic disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device such as a hard disk device having a read-ahead cache function.

[0002]

2. Description of the Related Art Conventionally, a magnetic disk device has a built-in disk controller, which controls read / write of data to / from a disk and data transfer with a host. The disk controller also has a cache function called a read-ahead cache. This read-ahead cache reads data from a sector ahead of a sector requested to be read by the host from a disk and stores the data in a buffer (cache memory). When a next read request occurs, the requested data is stored in the buffer. If a cache hit occurs, this data is taken out of the buffer and transferred to the host. As a result, the response speed to the host read request can be improved.

There is also a method called a segment cache in which a cache memory is divided into a plurality of blocks, and data in different areas on a disk is stored in individual blocks. In this case, one block corresponds to 1 on the disk.
It is often configured to have a capacity large enough to store all the sector data existing in the track.

However, the magnetic disk device having the segment cache function has the following problems. This will be described with reference to FIG.

In FIG. 1, Ta and Tn indicate different tracks on the disk to be read. Now, it is assumed that an ahead read (prefetch) process is being performed on the data of the track of Ta. If a next host request occurs during this prefetch operation and the requested data does not exist in the cache memory, that is, a cache mishit, the prefetch process is immediately interrupted,
Track seek for reading the requested data from the disk is performed. Therefore, in the cache memory block allocated to store the cache data at this time, a lot of free space is created in which the cache data is not written, and the cache hit rate for a subsequent read request is reduced. become.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and increases a cache data amount when a next host request occurs during a prefetch process by a read-ahead cache function. It is an object of the present invention to provide a magnetic disk drive capable of improving a hit ratio.

[0007]

According to the present invention, there is provided a magnetic disk drive comprising: a read / write head for reading / writing a signal from / to a disk;
A cache data storage unit for storing cache data, and further reading data ahead of data read from the disk through the read / write head in response to a read request from a host, and storing the cache data as the cache data. Means for reading data from the host; and when the next read request is issued from the host during the operation of the read-ahead means and the requested data is not stored in the cache data storage means, the disk and the read / write data are read. As a rotation waiting time, a time obtained by subtracting at least a time required for a track seek from a time required for a rotational positional relationship with the head to reach a target positional relationship corresponding to the read request from the current positional relationship is obtained as a rotational waiting time. The elapsed time from the occurrence of When there was example, the by interrupting the operation of the prefetch unit is made by and control means for performing control to perform a track seek operation.

[0008]

According to the present invention, the control means determines that a next read request is generated from the host during the prefetch operation by the prefetch means, and that the requested data is not stored in the cache data storage means (cache miss). In this case, the time obtained by subtracting at least the time required for the track seek from the total time required for the rotational positional relationship between the disk and the read / write head to reach the target positional relationship according to the read request from the current positional relationship. Calculate as rotation waiting time. At this time, the total time can be obtained based on the number of sectors between the sector on the disk being pre-read and the first sector requested to be read at the time when the read request is generated. The control means monitors the elapsed time since the read request occurred, and when the elapsed time exceeds the rotation waiting time, interrupts the operation of the prefetch means,
Thereafter, the track seek is started.

Therefore, according to the present invention, it is possible to continue the prefetching process longer by the rotation waiting time than before. As a result, the cache data amount can be increased and the cache hit rate can be improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a magnetic disk drive according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a disk and reference numeral 2 denotes a read / write head for writing and reading signals to and from the disk 1. 3 is a read / write head 2
Is a head amplifier that amplifies the write signal supplied to the read / write head 2 and the signal read by the read / write head 2. A read / write circuit 4 converts NRZ (Non-Retern to Zero) coded write data into a write signal for a read / write head, and NRZ codes a signal read by the read / write head 2. It is. Reference numeral 5 denotes a servo circuit that processes signals related to servo information read from the disk 1. Reference numeral 6 denotes a RAM for temporarily storing data transferred from the host device, data read from the disk 1, and the like.
The RAM 6 also has a cache memory area for a read-ahead cache function. The cache memory area is divided into a plurality of blocks, and each block can store a maximum of about one track of sector data read from the disk 1 by one ahead read (prefetch) process. ing. 7
Is the storage of data received from the host device in the RAM 6,
This is an HDC (hard disk controller) that controls the transfer of data stored in the RAM 6 to the host device and the input / output of data between the read / write circuit 4 and the RAM 6. 8 is the read / write head 2 and the disk 1
VCM (voice coil motor) for driving a carriage mechanism (not shown) that supports the movable member in the radial direction of the carriage. Reference numeral 9 denotes a VCM driving circuit for driving and controlling the VCM 8. Reference numeral 10 denotes a spindle motor for rotating the disk 1. Reference numeral 11 denotes a spindle motor drive circuit for controlling the drive of the spindle motor 10. Reference numeral 12 denotes a CPU that performs overall control of the above components. Reference numeral 13 denotes a ROM in which programs and data executed by the CPU 12 are stored.

Next, an operation typified by the magnetic disk device of the present embodiment will be described with reference to FIGS.

In FIG. 2, Ta and Tn indicate different tracks on the disk 1, respectively. Now Ta
It is assumed that an ahead read (pre-read) process has been performed on the sector data of the track No. The data read from the disk by this ahead read process is written to the cache memory area in the RAM 6 through the HDC 7 as cache data.

Thereafter, a next read request is generated from the host device, and if the requested data exists in the cache memory area, the target data is read from the cache memory area and transferred to the host apparatus.

Here, a problem occurs when the next host request occurs during the ahead read processing and the requested data is not stored in the cache memory area, that is, a cache mishit occurs.

In the magnetic disk drive of this embodiment, when such a host request occurs, the head read processing is not interrupted immediately, and the disk 1 and the read / write head 2 are not interrupted.
From the total time required for the rotational positional relationship with the current positional relationship to reach the target positional relationship according to the lead request,
At least the time obtained by subtracting the time required for track seek is obtained as the rotation wait time, and when the elapsed time from the occurrence of the read request exceeds this rotation wait time, control is performed so that the ahead read process is interrupted and the track seek is performed. Is performed.

That is, when the CPU 12 detects the occurrence of a read request from the host device during the ahead read process (step 31), it determines whether or not the requested data exists in the cache memory area (whether or not there is a cache hit). Judgment is made (step 32), and if there is a cache miss, the rotation wait time is calculated (step 3).
3).

The calculation of the rotation waiting time is performed as follows. First, the distance (the number of sectors) between the currently read ahead sector and the first sector requested to be read is determined, and the distance ta required for the disk 1 to rotate based on this distance is determined. Next, the track seek time tb required for the read / write head 2 to move from the current track to the track where the first sector requested to be read exists.
Ask for. Then, a value obtained by subtracting the track seek time tb from the previously obtained time ta is determined as the rotation waiting time.

Thereafter, a time waiting state is entered (step 34). When the elapsed time from the occurrence of the read request exceeds the rotation waiting time (step 35), the ahead read process is interrupted (step 36). Then, the cache data storage destination block in the cache memory area is switched (step 37), and track seek is performed (step 3).
8).

Therefore, according to the magnetic disk drive of this embodiment, when the next host request occurs during the ahead read processing, more cache data than the conventional method is stored in the cache memory area by the rotation waiting time. Can be stored. Thereby, the cache hit rate can be improved.

[0022]

As described above, according to the magnetic disk drive of the present invention, when the next host request occurs during the prefetch operation by the read-ahead cache function, the prefetch is longer than the conventional one by the rotation waiting time. Operation can be continued. As a result, the cache data amount can be increased, and the cache hit rate for a read request from the host can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a magnetic disk drive of one embodiment according to the present invention.

FIG. 2 is a diagram for explaining an operation when a next host request occurs during a pre-read operation in the magnetic disk device of FIG. 1;

FIG. 3 is a flowchart showing a procedure of the operation of FIG. 2;

FIG. 4 is a diagram for explaining an operation when a next host request occurs during a pre-read operation in a conventional magnetic disk device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Disc, 2 ... Read / write head, 3 ... Head amplifier, 4 ... Read / write circuit, 5 ... Servo circuit, 6
... RAM, 7 ... HDC (hard disk controller), 8 ... VCM (voice coil motor), 9 ... VCM
Drive circuit, 10: spindle motor, 11: spindle motor drive, 12: CPU, 13: ROM.

Continuation of the front page (56) References JP-A-3-116221 (JP, A) JP-A-57-172457 (JP, A) JP-A-3-54648 (JP, A) (58) Fields investigated (Int) .Cl. ⁶ , DB name) G06F 3/06 G06F 12/08-12/08 320

Claims (3)

(57) [Claims] A read / write head for reading / writing a signal from / to a disk; a cache data storage means for storing cache data; and a read / write head from the disk through the read / write head in response to a read request from a host. Read-ahead means for further reading data ahead of the output data and storing the read-out data as the cache data in the cache data storage means; a next read request is generated from the host during the operation of the pre-read means; Is not stored in the cache data storage means, the total time required for the rotational positional relationship between the disk and the read / write head to reach the target positional relationship according to the read request from the current positional relationship. , At least after subtracting the time required for track seek And control means for performing control so as to perform a track seek by interrupting the operation of the prefetching means when the elapsed time from the occurrence of the read request exceeds the rotation waiting time. A magnetic disk drive. 2. The magnetic disk drive according to claim 1, wherein the total time required for the rotational positional relationship between the disk and the read / write head to change from the current positional relationship to a target positional relationship according to the read request is represented by: A magnetic disk drive characterized in that the magnetic disk drive obtains the number based on the number of sectors between a sector on the disk that is being pre-read and the first sector for which a read request is made when a read request occurs. 3. The magnetic disk drive according to claim 1, wherein the cache data storage unit is divided into a plurality of blocks, and cache data is stored in each block of the cache data storage unit for each prefetch operation of the prefetch unit. A magnetic disk drive characterized by the above-mentioned.