JPH0588979A - Magnetic disk device - Google Patents

Abstract

PURPOSE:To improve the hit rate of a cache function by executing buffer management corresponding to the format of a read request from a host device in a magnetic disk device provided with the cache function. CONSTITUTION:In the magnetic disk device provided with an HDC 22, a sequential mode or a repeat mode is set up in a RAM 21 as a cache mode in accordance with a read request outputted from the host device, and when the sequential mode is set up, a host request data are transferred to the host device, the storage area of the data in a buffer 23 is released as an idle area and preread data are stored in the idle area. When the repeat mode is set up, the host request data are transferred to the host device and then the data are stored in the buffer 23.

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 having a cache function.

[0002]

2. Description of the Related Art In recent years, it has become common to incorporate a disk controller (HDC) in a magnetic disk device (HDD). This disk controller performs both reading / writing processing of data from the disk and transfer processing of host data to interface with the host device.

By the way, this disk controller usually has a cache function called "read-ahead cache" in order to improve the read performance. This cache function stores the sector data ahead of the sector requested by the host device in a buffer (cache memory), and if the host request data is in the buffer at the next data read (this is a hit) This is a process for reducing the disk rotation waiting time and improving the throughput by reading out from the buffer and transferring to the host device without reading from the disk.

FIG. 4 shows a conventional cache operation. When the read command is transferred from the host device, since there is no data in the buffer at the initial stage (steps B1 and B2), the host request data and the amount of ahead data (data before the host request) are stored in the disk. It is further read (step B3). Of the data thus read, the host request data is transferred to the host device (step B4), and the amount of ahead data (prefetched data) is stored in the buffer (step B5).
After that, if there is a read request and there is host request data in the buffer (if there is a hit), the data is fetched from the buffer (step B6) and transferred to the host device (step B7).

[0005]

Conventionally, buffer management in the cache function as described above has always been the same. In this case, the read operation of the disk data is different between the form of the host request, for example, the repeated read request and the sequential read request, so that the same buffer management has advantages and disadvantages in read performance.

That is, for example, in the buffer management in which after the data is transferred to the hoit device, the storage area of the data is released as an empty area and the prefetch data is always stored therein, in the case of repeated read requests (read requests for the same data). The hit rate is low. On the other hand, in the buffer management that holds the data that has been transferred as cache data, the hit rate becomes low at the time of a sequential read request (read request of continuous data).

The present invention has been made in view of the above points, and provides a magnetic disk device capable of increasing the hit rate of the cache function by performing buffer management according to the read request form of the host device. The purpose is to do.

[0008]

SUMMARY OF THE INVENTION The present invention is a magnetic disk device having a buffer for storing data read from a disk as cache data in response to a read request from the host device. According to the form of the read request, the first cache mode or the second cache mode is set. When the first cache mode is set, after the host request data is transferred to the host device, the data is transferred. The storage area of the buffer is released as an empty area, the prefetch data is stored therein, and when the second cache mode is set, after the host request data is transferred to the host device, the data is buffered. It is designed to be held at.

[0009]

According to the above configuration, the cache mode is switched to the first or second cache mode according to the form of the read request from the host device. Therefore, for example, a sequential read request (a continuous data read request)
Can increase the hit rate by managing the buffer that always stores the read-ahead data, and can increase the hit rate by managing the buffer that holds the data that has already been transferred for repeated read requests (read requests for the same data). it can.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic disk device according to an embodiment 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 device (HDD) incorporating a disk controller (HDC). In FIG. 1, a disk 11 is a recording medium and is rotated by driving a spindle motor 12.
The magnetic head 13 reads / writes data from / to the disk 11, and moves in the radial direction of the disk 11 by driving a voice coil motor (hereinafter referred to as VCM) 14. The head amplifier 15 is the disk 11
It has a function of amplifying a read signal from the magnetic head and a function of supplying a write signal to the magnetic head 13. The read / write circuit 16 performs data read / write processing under the control of a disk controller (hereinafter referred to as HDC) 22. The servo circuit 17 detects servo data (head positioning control data) from the read signal from the disk 11 and outputs this to the CPU 18. The CPU 18 controls the entire device (HDD). VCM drive circuit 19
Drives the VCM 14 under the control of the CPU 18. The spindle motor drive circuit 20 drives the spindle motor 12 under the control of the CPU 18. In RAM21,
A flag indicating a repeat mode / sequential mode described later is stored. Here, when the flag is set (when it is "1"), the repeat mode is shown, and when it is reset (when it is "0"), the sequential mode is shown.

The HDC 22 interfaces with the host device, and is incorporated in the device (HDD) here. The buffer 23 is a memory for storing the data read from the disk 11 as cache data in response to a read request from the host device. Next, the operation of the embodiment will be described.

The present invention has a sequential mode and a repeat mode as selectable cache modes. In the sequential mode, after the data is transferred to the host device, the storage area of the buffer for the data is released as an empty area and the prefetch data is stored there.
In the repeat mode, the data transferred to the host device is stored in the buffer as cache data, and the prefetching is completed when the buffer is full. Further, as a selection condition of the sequential mode and the repeat mode, if there are read requests a plurality of times (for example, three times) with the same sector as the start position, the repeat mode is set and the read request of the sector next to the last sector of the previous request is made. If it is set to sequential mode. The operation of the cache having the above two modes will be described below with reference to the flowcharts shown in FIGS.

First, at the initial stage, there is no data in the buffer 23, the flag of the RAM 21 is reset (flag "0"), and the sequential mode is set. In this state, when a read command is transferred from the host device, the HDC 22 causes the buffer 2
After confirming the state of 3 (step A1), a read command is issued to the CPU 18 to read the host request data and preread data (ahead amount of data) from the disk 11 (step A2). Of the data thus read, the HDC 22 transfers the host request data to the host device (step A3), and stores the prefetched data until the buffer 23 is full (step A4). This is the cache operation in the sequential mode.

When the next read request is from the host device, the HDC 22 determines the form of the read request (step A5). If it is a sequential read, it is first set in the RAM 21 through the CPU 18. Check which mode is in use (step A6). Here, if the set mode is the sequential mode (flag “0”), the HDC 22 searches the buffer 23,
If there is host request data, that is, if there is a hit (step A7), the data is read from the buffer 23 (step A8) and transferred to the host device (step A9). After that, until the mode is switched, HD
The C22 releases the storage area of the buffer 23 for the transferred data and stores the next prefetch data therein. In step A6, if the set mode is the repeat mode (flag "1"), the HDC 22 determines that the CPU
The sequential mode is set in the RAM 21 through step 18 (step A10), and the steps A2 to A4 described above are set.
Process.

On the other hand, in step A5, if the form of the read request is repetitive read, as in the above, first,
The mode set in the RAM 21 is confirmed through the CPU 18 (step A11). If the set mode is the sequential mode (flag “0”),
The HDC 22 issues a read command to the CPU 18 to read the host request data from the disk 11 (step A
12) and transfers this to the host device (step A1)
3). At this time, the HDC 22 reads the R through the CPU 18.
Set the repeat mode to AM21 (step A1
4) The transferred data is held in the buffer 23 as cache data (step A15). This is the cache operation in the repeat mode. If the set mode is the repeat mode in step A11 (flag "1"), the HDC 22 reads the host request data from the buffer 23 (step A16) and transfers it to the host device (step A17). After that, the HDC 22 holds the buffer full state and does not perform prefetching until the mode is switched.

As described above, the cache mode is switched to the sequential mode or the repeat mode according to the form of the read request from the host device. Therefore, for example, in a sequential read request (a continuous data read request), the hit ratio can be increased by managing the buffer that always stores the prefetched data, and in a repeated read request (the same data read request), the data transfer is completed. It is possible to increase the hit rate by managing the buffer that holds the data. As a result, it is possible to shorten the disk rotation waiting time and improve the throughput by utilizing the advantages of both modes.

In the above embodiment, the magnetic disk device with built-in HDC has been described as an example, but the present invention is not limited to this, and the same applies to the case where the HDC is outside the drive (HDD). The effect of is obtained. In addition to the magnetic disk device, the present invention can be applied to other I / O devices such as a magneto-optical disk device.

[0019]

As described above, according to the present invention, the cache mode is switched according to the form of the read request of the host device, and the buffer management optimal for each read is performed, so that the hit rate of the cache function is increased. Therefore, the read performance can be improved.

[Brief description of drawings]

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

FIG. 2 is a flowchart for explaining a cache operation of the same embodiment.

FIG. 3 is a flowchart for explaining a cache operation of the embodiment.

FIG. 4 is a flowchart for explaining a conventional cache operation.

[Explanation of symbols]

11 ... Disk, 12 ... Spindle motor, 13 ... Magnetic head, 14 ... VCM (voice coil motor), 15 ...
Head amplifier, 16 ... Read / write circuit, 17 ... Servo circuit, 18 ... CPU, 19 ... VCM drive circuit, 20 ...
Spindle motor drive circuit, 21 ... RAM, 22 ... HD
C (disk controller), 23 ... Buffer.

Claims (1)

[Claims] 1. A buffer for storing data read from a disk as cache data in response to a read request from a host device, and a first request depending on a form of the read request from the host device.
Mode setting means for setting the cache mode or the second cache mode, and when the first cache mode is set by the mode setting means, after transferring the host request data to the host device, The storage area of the buffer is released as an empty area, the prefetch data is stored therein, and when the second cache mode is set, the host request data is transferred to the host device and then the data is transferred to the above A magnetic disk device comprising: a buffer management unit for holding the data in a buffer.