JPS6046452B2 - Disk cache subsystem - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a disk cache subsystem, in particular, to stage data considered to be necessary on a magnetic disk device on a cache memory in advance when power is turned on. It concerns the disk cache subsystem that has been configured.

(2) Background of the Technology Directly accessible magnetic disk drives are widely used as mass storage devices in data processing systems.

However, accessing a magnetic disk device requires, for example, a head drive time or a disk rotation time, and requires an extremely long access time compared to accessing a normal main storage device. Therefore, recently, in order to speed up and improve the efficiency of input/output processing, a magnetic disk controller is installed between the magnetic disk controller and the magnetic disk adapter.
Disk cache that controls access data
Subsystems are considered. (3) Prior art and problems In a disk cache subsystem, input/output data to a magnetic disk device is cached and stored in memory, and the next time an input command for the same data is received, the data is actually sent to the magnetic disk device. In order to increase the speed, the previously stored data in the cache memory is transferred to the input request source without accessing the data.

At this time, which data on the magnetic disk device corresponds to the data on the cache memory is updated when data is written to the cache memory, and the extent table that holds management information for the data on the cache memory is updated. It is done by reference. Generally, the above cache memory and extent table are composed of volatile memory, so if the system is powered off at the end of the day's service, for example, the data on the above cache memory and extent table will be will disappear.

Therefore, when the power is turned on and the system is started the next day, there will be no data in the cache memory, and data will always be read from the magnetic disk device when an input request is issued. The need arose. Therefore, there was a problem that the cache memory was not utilized when the system started up. In order to solve the above problem, the inventor of the present application configured an extent table in nonvolatile memory, and when the system is powered on again, refers to the extent table and retrieves the data on the magnetic disk device that was accessed last time. Consideration was given to staging the data in cache memory in advance.

However, it turns out that there are some problems with this: First, the data on the magnetic disk device that is required when the power is turned on to start up the system, and the data on the magnetic disk device that is retained in cache memory when the power is turned off after service is completed. There is a large discrepancy with the data, and even with prestaging based on the above consideration, the address of the required data differs, so the cache memory is hardly utilized.

Second, if the system goes down due to a system failure, for example, the integrity of the contents of extent memory, which is made up of non-volatile memory, is guaranteed because it is not known at what point the processing will be interrupted. I can't do that.

Recover from the main system failure. When you restart the system, referring to the incomplete extent memory,
This is a problem that may lead to erroneous operations. (
4) Purpose of the Invention The present invention aims to solve the above problems and provides a system. The purpose is to enable effective use of cache memory even when starting up the system, allowing the entire system to start up quickly and smoothly.

(5) Structure of the Invention To achieve the above object, the present invention provides that the area on the magnetic disk device generally required at the time of system startup is, for example, VTOC (VOlumeTableOfCONten).
ts) Focusing on areas that are approximately fixed in a fixed format, we have developed a cache memory in which information read from a magnetic disk device or information written to the magnetic disk device is stored, and information stored on the cache memory. an extent table that stores information that associates the information stored in the data with information on the magnetic disk device; and a disk cache control device that controls information setting and reading of information in the cache memory and the extent table. In a disk cache subsystem equipped with a nonvolatile memory in which the contents of the extent memory are saved, and the extent memory when the cache memory becomes full for the first time after the system is powered on. a nonvolatile memory recording processing unit that records information stored in the nonvolatile memory in the nonvolatile memory, and a processor that reads information from the magnetic disk device onto the cache memory based on the information on the nonvolatile memory when the power is turned on again. It is characterized in that it is equipped with a staging processing section, and is configured to perform prestaging on the cache memory when the power is turned on.

(6) Examples of the invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the present invention, FIG. 2 shows an explanatory diagram of an example of processing operation of a nonvolatile memory recording processing section, and FIG. 3 shows an explanatory diagram of an example of processing operation of a prestaging processing section.

In the figure, 1 is the central processing unit, 2 is the magnetic disk control unit (
DKC), 3 is the disk cache ● subsystem,
4 is a magnetic disk adapter (DPCA), 5 is a magnetic disk device, 6 is a disk cache control device, 7 is a nonvolatile memory recording processing section, 8 is a prestaging processing section, 9 is a cache memory, and 10 is an extent table. , 11 is prestaging data flag section, 1
2 represents non-volatile memory.

The central processing unit 1 is a device that performs input/output to the magnetic disk device 5 and processes data.

The magnetic disk control device 2 decodes input/output commands from the central processing unit 1 and sends control signals and the like to the disk cache subsystem 3 and the like under its control. The disk cache control device 6 of the disk cache subsystem 3 manages the cache memory 9, the extent table 10, and the nonvolatile memory I river 2, and controls the entire disk cache subsystem 3. The non-volatile memory recording processing section 7 records the information of the extent table 10 necessary for pre-staging on the cache memory 9 at the next power-on on the non-volatile memory I river 2. Prestaging processing section 8
is activated when the system is started, and stages the data on the magnetic disk device 5 in advance to the cache memory 9 based on the information on the nonvolatile memory 12. The cache memory 9 is a memory in which input/output data to the magnetic disk device 5 is stored.
This is to speed up the processing of input/output instructions to the .

For example, the LRU (Least Recently Used) method is used to reuse the memory area of the cache memory 9. The extent table 10 is a control table that stores information that associates data on the cache memory 9 with data on the magnetic disk device 5, and in particular,
For example, if the data on the cache memory 9 has been staged by the prestaging processing unit 8 and has not been accessed by the central processing unit 1 even once since the power was turned on, each data It has a prestaging data (PD) flag section 11, which is a flag area for displaying each time. Non-volatile memory 12
has a capacity similar to that of the extent table 10, and stores the information in the extent table 10, especially the initial staged data after the power is turned on. storage information is recorded. In FIG. 1, the disk cache subsystem 3, which is incorporated into the system for the first time, operates as follows.

When the central processing unit 1 issues an input request to the magnetic disk device 5, the magnetic disk control device 2 reads data at the requested address from the specified magnetic disk device 5 and transfers it to the central processing unit 1. at the same time,
Disk cache ● Subsystem 3 cache
The disk cache controller 6 is requested to write the data onto the memory 9. The disk cache control device 6 sets data in an empty area on the cache memory 9, and also writes information indicating the location of the data on the magnetic disk device 5 in the extent table 10, such as device address cylinder. number,
Write the head number, record number, etc. Also, the non-volatile memory recording processing section 7 is called and the same information written in the exnotent table 10 is recorded in the non-volatile memory 12. This writing to nonvolatile memory 12 continues until all areas on cache memory 9 are filled with data. That is,
Cash me. When the memory 9 becomes full, the movement of information from the extent table 10 to the non-volatile memory 12 is stopped, and the non-volatile memory 2 contains data that is first staged to the cache memory 9 after power is turned on. Only information about the data will be recorded. Thereafter, when the service end time is reached, the power is turned off, and, for example, when the power is turned on again the next day, the disk cache subsystem 3 operates as follows. When the power is turned on, the prestaging processing section 8 of the disk cache control device 6 is first activated. The prestaging processing unit 8 determines whether or not valid data exists on the nonvolatile memo 1 river 2, and if valid data exists, accesses the magnetic disk device 5 based on the data, The data on the magnetic disk device 5 is written onto the cache memory 9. At the same time, the information on the non-volatile memory 12 is
Based on the result of actually accessing the magnetic disk device 5, the information is changed if necessary and written on the extent table 10. At this time, a flag indicating that the data set in the cache memory 9 is prestaging data is added to the extent table 10.
Set it in the prestaging●data●flag section 11 inside. This prestaging data flag is subsequently reset when the corresponding data on the cache memory 9 is accessed or replaced with other data in response to a request from the central processing unit 1. Ru.

At the time of resetting the flag, update information of the extent table 10 is simultaneously written into the nonvolatile memory 12 by the nonvolatile memory recording processing section 7. When the prestaging data flag is in the reset state, the nonvolatile memory 12 is not updated, so when all the data on the cache memory 9 is no longer in the prestaging state, the data on the nonvolatile memory 12 is not updated. Writing of information will be stopped. By doing so, prestaging information required at the next power-on is created and recorded in the nonvolatile memory 12. Since this recorded information is information that was used especially when the system was started, there is a high probability that the data associated with this information will be used at the next startup as well. By prestaging, the hit rate on the cache memory 9 can be improved. Note that since the LRU method is used for area allocation on the cache memory 9, the prestaging area is allocated preferentially to new area requests for the cache memory 9, and is preferentially allocated by other data. Since the prestaging data is replaced, there is no waste even if there is no access to the prestaging data.

An outline of the processing operation of the nonvolatile memory recording processing section 7 described above is as shown in FIG.

That is, there is an access to the cache memory 9,
When the extent table 10 is updated, the nonvolatile memory recording processing unit 7 first determines whether the current service is due to the first power-on. If it is the first power-on, that is, the first power-on after the disk cache subsystem is installed, then it is determined whether the cache memory 9 is full. If the cache memory 9 is already full, the process is immediately terminated. still,
If it is not full, the data written to the cache memory 9 is the first data written in the area, so the extent table 1
0 information is written into the nonvolatile memory 12 in preparation for prestaging when the power is turned on next time. If the current service is due to two or more power-ups,
The nonvolatile memory recording processing unit 7 determines whether the prestaging data (PD) flag on the extent table 10 corresponding to the accessed data on the cache memory 9 is on or off.

If it is off, the process ends immediately. If the PD flag is on, the update information of the extent table 10 is written to the nonvolatile memory I river 2, and the PD flag of the extent table 10 is turned off. The outline of the processing operation of the prestaging processing section 8 is as shown in FIG.

That is, when the prestaging processing unit 8 is activated by turning on the power, it first determines whether the contents of the nonvolatile memory 12 are valid. For example, when the power is turned on for the first time, the contents of the nonvolatile memory 12 are not valid, so the process ends. If it is valid, valid extent information is read from the nonvolatile memory 12, and based on that information, staging processing from the magnetic disk device 5 to the cache memory 9 is performed.
Furthermore, the extent table 10 is created based on the information in the nonvolatile memory 12 and the access information to the magnetic disk device 5. Next, extent table 10
All the PD flags in the prestaging data flag unit 11 of the prestaging data flag section 11 are turned on, and the process is ended. (7) Effects of the Invention As explained above, according to the present invention, data that is expected to be required at system start-up is prepared in advance on the cache memory, and the hit rate on the cache memory is reduced. can be improved to increase the efficiency of the system.

[Brief explanation of drawings]

FIG. 1 shows the configuration of an embodiment of the present invention, FIG. 2 is a diagram illustrating the processing operation of a nonvolatile memory recording processing section, and FIG. 3 is a diagram illustrating an example of the processing operation of the prestaging processing section. In the figure, 1 is the central processing unit, 2 is the magnetic disk control/control unit, 3 is the disk◆cache● subsystem, 4 is the magnetic disk adapter, 5 is the magnetic disk unit, 6 is the disk/cache control unit, and 7 is the nonvolatile 8 is a prestaging processing section, 9 is a cache memo 18, 10 is a storage table, 11 is a prestaging data flag section, and 12 is a nonvolatile memory.

Claims (1)

[Claims] 1. A cache memory in which information read from the magnetic disk device or information written to the magnetic disk device is stored, and information that associates the information stored on the cache memory with the information on the magnetic disk device. In a disk cache subsystem, the disk cache subsystem includes an extent table in which the extent memory is stored, and a disk cache control device that controls information setting and reading of information in the cache memory and the extent table. a non-volatile memory in which contents are saved; and a non-volatile memory in which information stored in the extent memory is recorded when the cache memory first becomes full after power is applied to the system. The prestaging section includes a recording processing section and a prestaging section that reads information from the magnetic disk device onto the cache memory based on the information on the non-volatile memory when the power is turned on again, and reads information onto the cache memory when the power is turned on again. A disk cache subsystem characterized by pre-staging.