JP2002182978A - Storage sub-system and information processing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform look-ahead of data by judging individual access states such as simple sequential access, sequential access to individual files in an environment of a multiple access operation a single logic device and a sequential access on the whole. SOLUTION: An existence density value to be the rate of the existence of logical tracks to which access has been made in a unit region from the total number of the logical tracks to which access has been made in the unit region which is constituted of the optional and continuous logical tracks on the logical device and from the total number of the logical tracks which constituted the unit region. The tendency of a change rate in the existence density value in a set which comprises the unit region area where a data block to be the input/ output object of a processor exists is analyzed, it is judged that access is a sequential access or a sequential access on the whole when the analysis result indicates that the obtained value increase is or is equal to or greater than a fixed value, look-ahead is performed concerning the data block in the vicinity of the data block where data to be the input/output object of the processor exist from an external storage device the read data are stored into a cache memory.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage subsystem having an external storage device and a control device therefor, and a control technique and a control device in an information processing system including a higher-level processing device in the storage subsystem. The present invention is effective when applied to a technique for controlling data prefetch from an external storage device to a cache memory in a control device.

[0002]

2. Description of the Related Art In a read-ahead control technique from an external storage device to a cache memory in a control device, a future access pattern is predicted based on history information of a past access pattern from a host processing device, and the prefetch is controlled. Things are common. In this prediction, accumulation of history information on past access patterns is important. JP-A-6-342401 and JP-A-11-53290 are examples of inventions related to such control.

[0003] The invention of JP-A-6-342401 is disclosed in
Examine multiple access requests recently accepted from the host processor, predict whether data following the address of the current access request will be accessed continuously, and activate prefetch control when it is determined that there is a possibility of access. Also, the present invention relates to a control device having a sequential access detecting means.

Similarly, the invention of Japanese Patent Application Laid-Open No. H11-53290 discloses that each time an input / output request is issued from a host processor,
A magnetic disk that stores the last address of an I / O request, and determines that the access is forward access and activates the prefetch control if the address of the current I / O request is the last address of the stored past I / O request + α. The present invention relates to a processing device.

[0005]

In recent information processing systems, the relationship between the number of connected upper-level processing units and control units and the storage capacity of the external storage unit is N: 1:
Assuming that n and the conventional one are M: 1: m, a relationship of N> M and n≫m holds. In particular, as indicated by n≫m, due to the improvement in the recording density of a magnetic disk device, which is a typical physical device constituting an external storage device, the storage capacity under one control device has been significantly increased. The data amount of the input / output request from the host processor has increased. Accordingly, the history information of the access pattern becomes enormous, and the processing time of the control device at the time of an input / output request increases due to the complicated management and search processing of the history information. I have.

[0006] In addition, due to the increase in storage capacity under one control unit, the size of a logical device has also increased.
The number of files existing per logical device is also increasing. Therefore, access to a plurality of files on one logical device frequently occurs at the same time, and when the history information is managed in units of logical devices, the history information is disturbed due to multiple access operations of one logical device. . Due to such disturbance of the history information, there is a problem that it is difficult to accurately predict an access pattern.

[0007] In a large-scale database, even if a local access is random access, if the entire database is viewed globally, continuous logical tracks in a logical device storing the database are completely formed. You may have access. That is, if attention is paid only to the state without considering the access pattern, it can be said that the sequential access has continuity. In the present invention, such a form is defined as "globally sequential access".

As described above, when it can be judged that the access is forward in general, read-ahead is performed from the external storage device, and high-speed data transfer and response to an input / output request from a higher-level processing device are enabled. It is necessary to do. However, if the history information of the access pattern as shown in the above-described conventional technique is used as the information for judging that the access is the general access, the control device at the time of the input / output request described above is used. However, there is a problem that the processing time increases and the history information is disturbed.

Therefore, by using means different from the prior art, simple sequential access, sequential access to each file in a multiple logical device multiple access operating environment,
The challenge is to be able to judge each access mode, which is a sequential access as seen in a large-scale database.

[0010]

In order to solve the above problems, the present invention mainly employs the following configuration.

[0011] An external storage device for storing data to be input / output by one or more higher-level processing devices using one or more physical devices, and exchanged between the higher-level processing device and the external storage device A control device that divides and manages data in appropriately sized data blocks and has a cache memory that temporarily holds the data blocks and controls input / output of the data blocks; and The control device determines, based on the total number of data blocks in the unit area where the data exists and the total number of data blocks requested to be input / output in the unit area where the data exists, the number of data blocks in the unit area where the data exists. Obtain the existence density value, which is the ratio of data blocks for which output requests have been made, and use simple sequential access and one logical device as seen in data duplication. Using the existence density value, a sequential access including a sequential access to each file in a multiple access operating environment or a global sequential access during a job execution processing period with a local random access found in a large-scale database is used. A storage subsystem that pre-reads from the external storage device a data block near a data block in which data to be input / output by the host processor exists.

[0012] Also, at least one higher-level processing device, an external storage device that stores data to be input / output by the higher-level processing device using one or more physical devices, A control device that divides and manages data exchanged with the device by appropriately sized data blocks and has a cache memory that temporarily holds the data blocks and performs input / output control of the data blocks;
In the information processing system including, the control device,
Based on the total number of data blocks in the unit area in which the data exists and the total number of data blocks in the unit area in which the data exists, there is an input / output request in the unit area in which the data exists. Calculating and storing the existence density value which is the ratio of the data blocks present, and when an input / output request from the higher-level processing device is issued to the data, the data to be input / output by the higher-level processing device. Analyze the trend of the rate of change of the existing density value in the unit area set including the unit area where the block exists, and judge whether the result of the analysis indicates an increase or a certain value or more,
If the determination result is true, an information processing system that prefetches a data block near a data block in which data to be input / output by the higher-level processing device exists from the external storage device and stores the data block in the cache memory .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A storage subsystem (comprising an external storage device and its control device) and an information processing system (a storage subsystem including a higher-level processing device) according to an embodiment of the present invention are described below. This will be described in detail with reference to the drawings. First, an outline of an embodiment of the present invention will be described. Unlike a conventional technique of predicting an access mode using history information of an access pattern, a simple forward access at the present time and a multiple access operation environment of one logical device are different. It is an object of the invention to be able to judge each access mode of sequential access to each file at the same time and global access as seen in a large-scale database and to prefetch data, and the current access is a sequential access. To determine if there is
The upper processor counts the number of logical tracks accessed in a unit area composed of arbitrary continuous logical tracks on a logical device that stores data to be input / output, and calculates the total number of logical tracks accessed in the unit area. From the total number of logical tracks constituting the unit area, an existence density value which is a ratio at which the accessed logical track exists in the unit area is calculated, and a unit area including a data block to be input / output by the processing apparatus is included. The trend of the rate of change of the existence density value within the unit area set is analyzed.

If the analysis result indicates an increase or a predetermined value or more, the access is determined to be a forward access or a global forward access, and the data in the vicinity of the data block in which the data to be input / output to / from the processing device exists. The block is read ahead from the external storage device and stored in the cache memory.

Here, the access mode will be described by way of example (see FIGS. 1 and 2). In the simple sequential access, for example, data is sequentially read from logical track # 0 to #n by a data duplication process. This is an access mode at the time of reading when data is transferred to another external storage device. In the multiple access operation environment, sequential access to a file is performed when a plurality of files are allocated to one logical device and a plurality of processing devices share the logical device.
3 are sequentially read, and logical track # 90 is included in file F.
To # 95 are sequentially read (for the logical device, the access from the logical tracks # 0 to # 3 to the logical tracks # 90 to # 95 is not a simple sequential access).

In the global sequential access, time-series reading is performed in logical tracks # 0 to # 5 and logical track # 1.
Although it is not a simple sequential access such as 0 to # 15, logical tracks # 20 to # 25, and logical tracks # 6 to # 9, when observed over the entire execution processing period of a certain job, Is an access mode that can be considered as a global access because the logical tracks # 0 to # 25 have been read. In other words, in a large-scale database, even if the local database is viewed randomly, even if the entire database is viewed globally, it is possible to access all the continuous logical tracks in the logical device storing the database. May be. That is, if attention is paid only to the state without considering the access pattern, it can be said that the sequential access has continuity. In the present invention, such a form is defined as "globally sequential access".

As an example of read-ahead for such three access modes, in the first access mode, a simple sequential access, if there is an access command to the logical tracks # 0 to # 5, the access to the logical tracks # 6 to # 6 is performed. Tracks can also be read ahead. In the second and third access modes, the read access is not performed in the above-described example in the order of the logical track in the time series.
In order to read ahead, it is necessary to devise an embodiment of the present invention as described below.

[Explanation of the Overall Configuration of the Information Processing System] The information processing system shown in FIG. 1 includes a processing device 10 for calculating information and the like, a channel 11 for input / output control such as data transfer, and an external storage device 13. And a control device 12 for controlling these devices. Here, what is composed of the external storage device 13 and the control device 12 is called a storage subsystem. Further, the control device 12 has a recording / reproducing function for the control information memory 122 for storing control information used when performing control, and a function of having an internal clock and capable of acquiring time. This information processing system
Channel 11 and control device 12 according to the instruction of the processing device 10
External storage device 13 via the cache memory 124 in the
It issues a data input / output command to the logical device 132 defined in the device. The data requested to be input / output from the processing device 10 is normally stored in the logical track 2 shown in FIG.
Every 0 is stored in the cache memory 124.

The external storage device 13 shown in FIG. 2 is composed of one or more physical devices 131. Further, the processing device 10
The data to be input / output is managed on a logical device 132 basis. The logical device 132 is assigned by the control device 12 to a group of one or more physical devices 131.
The logical device is defined in a form in which the logical device is divided in a logical range for control, and each divided area is distributed to each physical device.

In general, an area obtained by dividing one logical device in a logical range for control is defined by a logical track 20.
The logical track 20 is composed of a logical record 21 which is a minimum unit obtained by dividing one logical device into a logical range for control. The processing device 10 specifies a logical track address and a logical record address in the logical device 132 in which the data to be input / output exists, and issues a data input / output command to the control device 12.

The logical track 20 stored in the cache memory 124 is usually stored in the LRU (Least Recently Used) using the cache directory information table 123 installed in the control memory 122.
se) It is managed by the method. The LRU method is a known technique and is widely used as a paging management method for memories.

FIG. 3 shows the structure of the cache directory information table 123. Presence density value management table 30
Is a device address 31 and a unit area management table 32
It consists of. The unit area management table 32 is composed of unit area addresses 33, existence density values 34, existence density value storage times 35, and unit area cache hit logical track bit map tables 36, which are information on each unit area. Here, the existence density value, which will be described in detail later, refers to the ratio of the existence of the accessed logical track in the unit area in the logical device.

The unit area cache hit logical track bit map table 36 stores the logical track stored in the cache memory 124 in the logical device as one logical track.
This table is managed by bits. If a bit is ON, it indicates that the logical track of the corresponding address has become an input / output target of the processing device 10 on the cache memory 124. When the bit is turned on, the processing device 10
And the control unit 12 outputs data from the external storage device 13 and pages in the cache memory 124 in response to a data input request from the processing device 10. is there.

The block queue 37 relating to the logical track manages the information block 38 relating to the logical track in a queue structure.
The page connected to the U side is paged out. The information block 38 relating to the logical track stores control information for managing the logical track on the cache memory 124.

"Explanation on existence density value" processing unit 10
Is the logical device 1 where the data to be input / output exists
A logical track address and a logical record address in 32 are designated, and a data input / output command is issued to the control device 12. In response to an instruction from the processing device 10, the control device 12 determines whether a logical track to be input / output exists in the cache memory 124 or not in the cache directory information table 12.
3 is searched for the cache hit logical track bit map table 36 in the unit area and the block queue 37 related to the logical track. If there is, the corresponding logical record in the corresponding logical track address on the cache memory 124 is processed as an input / output target. If the physical device 131 does not exist in the cache memory 124,
Then, a logical record in the logical track is input and then the relevant logical record in the relevant logical track address on the cache memory 124 is processed as an input / output target.

The control device 12 includes a cache memory 124
When processing is performed on the upper logical record 21, the information block 38 on the target logical track is stored in the block queue 37 on the logical track in the MRU (M
ostRecentlyUse).

The control unit 12 defines a value L indicating a certain number of continuous logical tracks, logically divides the logical device 20 by the value L, and uses this as a unit area. Therefore, the control device 1
2 divides the logical track address α requested to be input / output from the processing device 10 by the value L, and obtains the quotient as the address (N) of the unit area.

The control unit 12 searches the unit area cache hit logical track bitmap table 36 in the unit area management table 32 corresponding to the address N of the unit area, and obtains the total number of cache hit logical tracks. The total number of obtained cache hit logical tracks is represented by a value L.
And the quotient is obtained as the presence density value D (N, T) at the current time T at the address (N) of the unit area where the logical track address α exists. That is, referring to FIG.
D (Density) = the number of hit logical tracks / L, and indicates the hit ratio of the logical tracks for each continuous logical track number L. At this time, the address is replaced with # α for each logical track and the address for each track number L. N.

Further, the control device 12 sets the presence density value D (N) at the current time T at the address (N-1) of the unit area adjacent to the address (N) of the unit area where the logical track address α exists. −1, T). FIG. 4 shows the relationship between the address (N) and the address (N-1) of the unit area.

"Explanation of Processing for Determining Whether Prefetching is Possible" First, the outline of prefetching will be qualitatively described with reference to FIG. As described above, unlike the prior art in which the access order is determined by checking whether or not the access is performed for each logical track number, the addresses N, NI,... Of the unit area for each logical track number L are assumed. The ratio of the number of hits of the logical track to L of the address is defined as an existence density value D. The unit area address is set on the horizontal axis, and the existence density value D
The relationship between the current time T and the vertical axis is shown as a solid line graph in FIG. The D value of the address N included in the logical track # α is indicated by the point A, and the D value of the address (N-1) is indicated by the point B.
(Addresses below (N−n)) have reached saturation at which the number of hits, that is, the D value is 1. A D value of 1 indicates that all logical tracks at the unit area address have been hit.

Further, it expressed a similar relationship in an earlier T ₁ than the current time, so that the dotted line graph in FIG. At the address N, the D value is at the point E, and the D value at the address (N-1) is F.
Indicated by dots. In the illustrated example of FIG. 6, the D value at the point A is larger than the D value at the point E at the address N, and the number of hits at the address N is increasing.

In FIG. 6, in the solid line graph at the current time T, the addresses with lower numbers are illustrated in a linear relationship having a higher hit ratio. Therefore, if the address number is gradually reduced, the address reaches a young address at which the D value becomes 1. The address whose D value is 1 is (N-n)
Where n satisfies this relationship is the slope between points A and B,
It is a numerical value that can be easily obtained based on the address N and the total number L of logical tracks.

In the above description, the state where the D value is 1 is used as one criterion. However, the value is not limited to D = 1. May be used as a reference value instead of. Therefore, n based on S may be calculated.

Therefore, as an example of the pre-read execution determination process, if the D value at the address (N-1) at the current time T is equal to or larger than the threshold value S, a track near the logical track # α is pre-read. (If the D value of the address (N-1) is 1, it means that it is a simple sequential access, so that the prefetching process is of course performed). and of being processed or the propriety conditions lookahead implementing comparisons, for each D value of the address (N-1) in the previous time T _1, which will be described later in detail.

FIG. 5 is a flowchart showing a process for judging whether or not to perform prefetching. According to FIG. 5, step 50
1, the processing apparatus 10 sets the logical track address α in the logical device 132 in which the data to be input / output exists.
And a logical record address, and issues a data input / output command to the control device 12. In response to a command from the processing device 10, the control device 12 performs input / output processing on the logical track address α. At that time, in step 502,
Existence density value D (N, T) at the current time T at the address (N) of the unit area where the logical track address α exists
Ask for.

Similarly, in step 503, the existence density value D (N-1) at the current time T in the address (N-1) of the unit area adjacent to the address (N) of the unit area where the logical track address α exists. , T). In step 504, it is determined whether or not the existence density value D (N-1, T) satisfies the following equation (1). If the judgment result is true, the access mode is recognized as the sequential access. Here, the existence density value D (N-1, T) is compared with the threshold value S. The comparison in step 504 is processed by a program, and the setting of the threshold value S at that time is performed by an operation provided in the control device 12. It is set so that it can be changed to an appropriate value by means.

In step 505, prefetching is performed on the area adjacent to the logical track address α and the area adjacent to the area near the logical track address α. In this case, the area adjacent to the vicinity of the logical track address α is the address of the unit area (N) and the address of the unit area (N + 1).

D (N−1, T) ≧ threshold value S (1) On the other hand, if the judgment result is false, in Step 507, the value of the unit area adjacent to the address (N−1) of the unit area is determined. D (N−2, T), which is the existence density value at the current time T at the address (N−2), is obtained.

Next, in step 508, D (N−1,
T ₁ ), D (N−2, T ₂ ) and D (N−1, T), D (N−2, T) determined in step 507, satisfy the following expression (2): Judge. If the result of the determination is true, it is determined in step 509 whether the following expression (3) is satisfied. If the result of the determination is true, the access mode is recognized as a forward access, and the process continues to step 505. .

D (N−1, T)> D (N−1, T ₁ ) and D (N−2, T) ≧ D (N−2, T ₂ ) (2) D (N− (2, T) ≧ threshold value S (3) On the other hand, if the judgment result in step 509 is false, in step 510, a model in which the rate of change of the existence density value is a constant value A is defined. Is applied, and (N−n) that satisfies the following equation (4) is calculated.

Next, in step 511, it is determined whether the value n of the address (N-n) of the unit area does not exceed the upper limit Z (the difference between the address (N) and the address (N-n)). If the gap is too far beyond the upper limit Z, there is a possibility that another file address is being looked at. Therefore, a certain upper limit Z is set for the gap.) If the judgment result is true, In step 512, D (N-n, T), which is the presence density value at the current time T at the calculated address (N-n) of the unit area, is obtained.

Next, at step 513, the existence density value D
If (N−n, T) satisfies the following equation (5),
The current access is generally recognized as a forward access, and the process continues to step 505.

D (N−n, T) = A × (N−n) + B = threshold value S (4) where A = D (N−1, T) −D (N−2, T) , B
= D (N−1, T) − (A × (N−1)) D (N−n, T) ≧ threshold value S (5) Finally, at step 506, at times T, D (N, T),
D (N-1, T), D (N-2, T), D (N-n,
T) to the corresponding unit area management table 32
To memorize.

As described above, the embodiments of the present invention include those having the following configurations and functions. That is, in order to determine the current global sequential access, a logical track accessed in a unit area composed of arbitrary continuous logical tracks on a logical device that stores data to be input / output by the host processor. From the total number of logical tracks accessed in the unit area and the total number of logical tracks constituting the unit area, a presence density value which is a ratio of the number of logical tracks accessed in the unit area is calculated. The density value is used in the following way.

When an I / O request is issued from the host processor, the logical track address α for which the I / O request was made
And the unit area (N)
D (N, T) which is the existence density value at the current time T in
Ask for. Also, the time T and the existence density value D (N,
T) is stored as control information managed for each unit area.

Similarly, D (N-1, T), which is the existence density value at the current time T in the unit area (N-1) adjacent to the unit area (N) where the logical track address α exists, is obtained.

At this time, if the following condition (1) is satisfied, sequential access is performed, and prefetching is performed on the area adjacent to the logical track address α and the area adjacent to the logical track address α.

D (N−1, T) ≧ threshold value S. Condition (1) On the other hand, if condition (1) is not satisfied, the current value in the unit area (N−2) adjacent to the unit area (N−1) The existence density value D (N−2, T) at the time T is obtained. D (N-
1, T) and D (N−2, T) are the stored D
After satisfying the following condition (2) between (N-1, T ₁ ) and D (N−2, T ₂ ), if the following condition (3) is satisfied, the access is forwarded. The pre-read is performed on the area near the logical track address α and the area adjacent to the logical track address α.

D (N−1, T)> D (N−1, T ₁ ) and D (N−2, T) ≧ D (N−2, T ₂ ) Condition (2) D (N− (2, T) ≧ threshold value S. Condition (3) When condition (2) is satisfied but not condition (3), a model in which the rate of change of the existence density value is constant is defined as a model. Applying and satisfying the following condition (5), (N−
n) is calculated. At this time, if the value n does not exceed the upper limit value Z, D (N-n, T) which is the existence density value at the current time T in the calculated unit area (N-n) is obtained.

If the presence density value D (N−n, T) satisfies the following condition (5), the vicinity of the logical track address α is globally forward-accessed, and the vicinity of the logical track address α is And prefetching is performed on an area adjacent to the vicinity of the logical track address α.

D (N−n) = threshold value S... Condition (4) D (N−n, T) ≧ threshold value S... Condition (5) Further, time T, D (N−1, T), D (N-2, T),
Each of D (N−n, T) is stored as control information managed for each unit area. When an input / output request is issued from a higher-level processing device, the above-described means is implemented.

The size of the unit area, each constant, and the like described in the above means are arbitrary values, and the arbitrary values do not depart from the scope of the present invention. Further, in the above means, in order to make the concept easy to understand, the data is a logical device for storing data, and the data block is a logical track. However, even if these are handled in different units, they deviate from the present invention. Not something.

In determining the unit area (N−n), the model of the rate of change of the existence density value described in the above means does not always indicate the rate of change of the constant value. A general model can be applied, and a method of setting n to a fixed value is also possible, and using any method does not depart from the present invention.

The conditions (1) to (5) of the above means are only one of the methods for analyzing the trend of the rate of change of the existence density value, and the existence density value is determined using another method. Analyzing the trend of the rate of change of does not depart from the invention.

[0055]

According to the present invention, when it can be judged that the access is forward in general, read-ahead is performed from the external storage device, and high-speed transfer and response to the input / output request from the higher-level processing device are performed. Can be possible.

In addition to simple sequential access, the present invention can be applied to a multiple access operation of one logical device in which accesses to a plurality of files on one logical device occur at the same time.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an information processing system including a host processing device, an external storage device, and a control device.

FIG. 2 is a diagram illustrating a configuration of an external storage device.

FIG. 3 is a diagram related to a control information memory in the control device.

FIG. 4 is a diagram showing an observation positional relationship for analyzing a rate of change of an existence density value.

FIG. 5 is a flowchart illustrating a method of determining a forward access from a presence density value.

FIG. 6 is an explanatory diagram of a method of determining a forward access using an address of a unit area and an existence density value.

[Explanation of symbols]

Reference Signs List 10 processing device 11 channel 12 control device 13 external storage device 121 control unit 122 control information memory 123 cache directory information table 124 cache memory 131 physical device 132 logical device 20 logical track 21 record 30 existence density value management table 31 device address 32 unit Area management table 33 Address of unit area 34 Presence density value 35 Presence density value storage time 36 Cache hit logical track bit map table in unit area 37 Block queue related to logical track 38 Information block related to logical track

Continued on the front page (72) Katsuhiro Kawaguchi, 2880 Kozu, Odawara City, Kanagawa Prefecture Storage System Division, Hitachi, Ltd. (72) Inventor Hiroaki Konuma 2880 Kozu, Odawara-shi, Kanagawa F-term in the Storage Systems Division, Hitachi, Ltd.

Claims (4)

[Claims] An external storage device for storing data to be input / output by one or more high-level processing devices using one or more physical devices, and exchanges between the high-level processing device and the external storage device And a control device that controls the input / output of the data block by dividing and managing the data to be performed in data blocks of an appropriate size and having a cache memory for temporarily holding the data block. The control device, based on the total number of data blocks in the unit area where the data exists and the total number of data blocks requested to be input / output in the unit area where the data exists, The density of the data blocks that had an I / O request was calculated, and a simple sequential access and one logical device as seen in data duplication Access to each file in a multi-access operating environment of the application, or global access during a job execution process with local random access found in a large-scale database, A storage subsystem, wherein a data block near a data block in which data to be input / output by the host processor exists is read ahead from the external storage device. 2. An external storage device for storing data to be input / output by one or more high-level processing devices using one or more physical devices, and exchanges between the high-level processing device and the external storage device And a control device that controls the input / output of the data block by dividing and managing the data to be performed in data blocks of an appropriate size and having a cache memory for temporarily holding the data block. The control device, based on the total number of data blocks in the unit area where the data exists and the total number of data blocks requested to be input / output in the unit area where the data exists, Calculating and storing an existence density value which is a ratio of data blocks having an input / output request in the upper processing unit; When the occurrence of the data block, the trend of the rate of change of the existence density value in the unit area set including the unit area in which the data block to be input / output of the higher-level processing apparatus exists, and the result of the analysis Is judged to be true or false indicating whether the value indicates an increase or a certain value or more, and if the judgment result is true, the data block near the data block where the data to be input / output of the higher-level processing device exists is referred to as the data block. Read ahead from an external storage device,
A storage subsystem for storing data in the cache memory. 3. An at least one high-level processing device, an external storage device that stores data to be input / output by the high-level processing device using at least one physical device, the high-level processing device, and the external storage A control device that divides and manages data transmitted and received with the device by appropriately sized data blocks and has a cache memory that temporarily holds the data blocks and performs input / output control of the data blocks. In the information processing system provided, the control device, based on the total number of data blocks in the unit area where the data exists and the total number of data blocks that have been input / output request in the unit area where the data exists, The existence density value, which is the ratio of data blocks for which input / output requests exist in the unit area where the data exists, is calculated. Access to each file in a multiple access operating environment of one logical device, or global access during job execution processing with local random access found in a large-scale database. An information processing system, wherein a determination is made using the existence density value, and a data block near a data block in which data to be input / output by the host processing device exists is read ahead from the external storage device. 4. An at least one high-level processing device, an external storage device that stores data to be input / output by the high-level processing device using at least one physical device, the high-level processing device, and the external storage A control device that divides and manages data transmitted and received with the device by appropriately sized data blocks and has a cache memory that temporarily holds the data blocks and performs input / output control of the data blocks. In the information processing system provided, the control device, based on the total number of data blocks in the unit area where the data exists and the total number of data blocks that have been input / output request in the unit area where the data exists, Calculates and stores the existence density value, which is the ratio of the presence of a data block having an input / output request in the unit area in which When an input / output request is issued for the data, the trend of the rate of change of the existence density value in the unit area set including the unit area in which the data block to be input / output of the upper processing unit exists is analyzed. It is determined whether the result of the analysis indicates an increase or a value equal to or more than a certain value. If the result of the determination is true, the vicinity of the data block in which the data to be input / output by the higher-level processing device exists. An information processing system, wherein the data block is read ahead from the external storage device and stored in the cache memory.