WO2000007105A1 - Computer system - Google Patents

Abstract

Data written in variable length format by a first computer is written in fixed length format into a physical volume by a controller according to a specified logic. A second computer reads out the data in fixed length format from the physical volume and extracts variable length data according to the same specified logic. The data written by the first computer can thereby be used by the second computer. Data read out by the second computer can be used similarly by the first computer.

Description

 Description Computer system Technical field

 The present invention relates to a computer system, and more particularly to a computer system including a plurality of computers and a storage device shared by the computers. Background art

Some of the host computers (especially large computers) have magnetic disk units with variable-format data formats. These host computers have a variable-length data access interface called CKD interface to access the magnetic disk device. Conventionally, variable-length record formats have been realized as they are on physical storage devices. A technique called RAID, which achieves high reliability by improving the parallelism of data and improving the performance by adding redundancy to the data, is becoming common. This approach the United States, Burke Rei, mosquito Li off Orunia University of the putter source emissions (p _a tterson), etc., the United States computer Society data management expert group Technical Report (P roc. ACMSIGMOD) 1 9 8 8 years June It has been spreading rapidly since the announcement of the “Case of Redundant Array of Inexpensive Disks (RAID)”.

Literature: As described in “Mainframe '98”, Nikkei BP, pl 26-130, a storage system to which RAID technology is applied uses an FBA (Fixed Block Architecture) format. A magnetic disk device having a fixed-length data format called a mat is used, and a SCSI interface (or a SCSI interface) is used as an interface to access the disk device. SCSI protocol) is used. Therefore, the host computer accesses variable-length data via the CKD interface. . In a storage system using an FBA-type magnetic disk internally, when data is written, the format is changed from variable-length format to fixed-length format, and data is read. In such a case, a format conversion mechanism is provided for converting a fixed-length format into a variable-length format. As an example of such a format conversion mechanism, for example, Japanese Patent Application Laid-Open No. H6-155057 is known.

 In recent years, many computing centers have a system configuration in which host computers and open hosts such as UNIX servers and PC servers are mixed. In such a configuration, there is a high demand for facilitating the management of the storage system and reducing the total storage cost. To address this, variable-length and fixed-length access interfaces, such as those found in Mainframe '98, Nikkei BP, pl45 or pl51 Storage systems with both interfaces have been developed. On the other hand, recently, a host computer with a built-in disk device that has an SCS I interface has emerged. For example, in the server described in “Mainframe '98”, Nikkei Business Publications, p. 53-54, an FBA-formatted disk device is built in the housing of the host computer. A processor called SAP interprets variable-length data access commands (CCW: Channel Command Word chain) generated by the OS, and issues fixed-length data access commands. (SCSI command) and execute input / output processing to the internal disk. In this built-in disk, variable-length data is embedded in a fixed-length format, and format conversion is performed by SAP. The advantage of converting the CCW generated by the OS into the CSSI command by the SAP is that it is not necessary to change the OS or the application program.

 The server relates to a built-in disk, but by applying the conventional technology, it becomes possible to connect an external storage system having a fixed-length access interface to the host computer. Since such external storage devices are provided by many vendors, the user has a wide range of choices according to price, performance, and reliability, and the advantages are very large.

The external storage device is assumed to be shared by multiple host computers. This also means that the storage device is provided outside the host computer housing. However, since the above-mentioned conventional technology is originally related to a built-in disk, it does not consider sharing data.

 The issues in sharing data are described below.

 Both fixed-length and variable-length access interfaces as described in “Mainframe '98”, Nikkei BP, pl45 or pl51. Even if a host computer with a fixed-length access interface and a host computer with a variable-length access interface are connected to a storage system with The format of the data, that is, the method of converting between the variable format and the fixed format, is common between the host computer with the ace and the storage system. Without it, data cannot be shared. That is, the data written to the storage device from the host computer having the variable-length access interface is read from the main frame having the fixed-length access interface, or vice versa. There is a problem that cannot be done.

 An object of the present invention is to allow data stored in an external storage device to be shared between a host computer having a fixed-length access interface and a host computer having a variable-length access interface. It is to be. Disclosure of the invention

In order to achieve the above object, a computer system according to the present invention has an access interface to a first logical volume formatted by a variable-length format. A first computer, an interface for accessing a second logical volume formatted by the fixed-length format, and the second logical volume Variable-length data is extracted from the fixed-length data read out from the fixed-length data according to a predetermined logic, and the variable-length data is converted into fixed-length data to be written into the second logical volume according to the predetermined logic. A second computer having a means, a physical volume formatted by a fixed-length format, connected to the first and second computers, 1 logical volume to the predetermined logic Strange off O over Ma Tsu door to a fixed-length off O over Ma Tsu by Ri off O over Ma in Settsu door has been the physical volume I In other words, there is provided a control device that matches the address of the second logical volume with the address of the physical volume.

 The controller writes the data written by the first computer in the variable-length format to the physical volume in a fixed-length format with a predetermined logic. Further, the second computer reads out the data of the fixed-length format from the physical volume and extracts the variable-length data by the predetermined logic. As a result, the data written by the first computer can be used by the second computer.

 In addition, the control unit writes the data that the second computer converts the variable-length data into fixed-length data according to a predetermined logic and writes the converted data to the physical volume unit in a fixed-length format. Further, the control device reads the data of the fixed-length format from the physical volume according to a request of the first computer, converts the data into variable-length data by the predetermined logic, and converts the data into variable-length data. Pass this variable length data to the calculator. This allows the data written by the second computer to be used by the first computer. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a configuration diagram of a computer system in the first embodiment. FIG. 2 is a schematic explanatory diagram of the first embodiment.

 FIG. 3 is a configuration diagram of the storage device.

 Figure 4 shows the track format of variable-length data.

 Figure 5 shows the fixed-length data track format.

 FIG. 6 is an explanatory diagram of a format conversion method between variable-length data and fixed-length data.

 FIG. 7 is a flowchart of a format conversion mechanism included in the control device and the host computer.

 FIG. 8 is a flowchart of the write processing in the format conversion mechanism of the host computer.

FIG. 9 is a flowchart of a fixed-length data access mechanism included in the control device. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

 FIG. 1 shows a configuration diagram of a computer system according to the present invention. In the present invention, one or more host computers 110 having a variable-length access interface and one or more host computers 110 having a fixed-length access interface are provided. It is composed of one or more storage systems 150. Upon receiving an input / output request from the application program, the host computer 100 generates a command group (CCW chain) for accessing the storage device of the variable-length format. File access mechanism 103 and the CCW chain generated by the file access mechanism 103 to execute input / output processing with the storage system 150. Seth mechanism 104 exists.

 On the other hand, the host computer 110 receives a request for input / output from the application program and generates a file access request for generating a CCW chain for accessing a storage device of a variable-length format. Interprets the CCW chain, converts the format between variable-length data and fixed-length data, and generates SCSI commands to access fixed-length storage devices. A format conversion mechanism 111 and a fixed-length data access mechanism for executing I / O processing by executing SCSI commands generated by the format conversion mechanism 112. It has 1 1 4

 The storage system 150 includes a physical volume 128 for storing data, and a control device 12 for controlling input / output processing between the physical volume 128 and the host computer 100 or 110. Consists of 0.

 The physical volume 128 is a fixed-length format storage device, and is connected to the control device 120 by a storage device path 127. The control device 120 executes input / output processing for the physical volume 128 using the storage device access mechanism 126. An example of a physical volume 128 is an FBA disk with a SCS I interface or a fiber interface.

The controller 120 and the host computer 100 are connected by the host path 130, and the CCW chain issued from the host computer 100 is acceptable. It is interpreted by the variable length data access mechanism 122 and the input / output processing of the variable length volume is executed. In the present invention, an actual example of the host path 130 is ESC0N or a fiber channel, and the variable length volume is assumed to be a CKD disk.

 On the other hand, the controller 120 and the host computer 110 are connected by the host path 140, and the SCSI command issued from the host computer 110 has a fixed-length data access mechanism. The input / output processing to the fixed-length volume is executed. In the present invention, the actual example of the host path 130 assumes an SSI bus or a fiber channel, and the fixed-length volume assumes an FBA disk.

The cache memory 123 is a memory for temporarily storing data on the physical volume 128.

 Since the physical volume 128 is a fixed-length format, the variable-length data access mechanism 122 executes format conversion between the fixed-length format and the variable-length format. There is a need. This processing is executed by the format conversion mechanism 124.

 The host computer 100 recognizes the variable length volume to be accessed as a logical volume 200a, and the host computer 110 recognizes the fixed length volume to be accessed. The resume is recognized as logical volume 200b. These situations will be described with reference to FIG.

The logical volume 200a recognized by the host computer 100 is a storage device that is formatted by a variable-length format, and is used to access target data. The host computer 100 uses the variable-length data access mechanism 104 to determine the number of the logical volume 200a and the address of the data to be accessed on the logical volume 200a. Specify according to the access interface of the variable-length volume. The control device 120 converts the variable-length data of the logical volume 200a into a physical volume 128 having a fixed-length data format by the format conversion mechanism 124. Perform format conversion. That is, when there is an access request from the host computer 100, the number of the specified logical volume 200a and the access address are converted to the corresponding address on the physical volume 128. I do. The format conversion method between variable-length data and fixed-length data and the correspondence between addresses realized by the format conversion mechanism 124 will be described later.

 On the other hand, the logical volume 200b recognized by the host computer 110 is a storage device that is formatted in a fixed-length format, and is used to access target data. The host computer 110 uses the fixed-length data access mechanism 114 to determine the number of the logical volume 200b, the address on the logical volume 200b, and the like. Specify according to the fixed-length volume access interface. Actually, this logical volume 200b is the physical volume 128 itself. That is, the address on the logical volume 200b and the address on the physical volume 128 match. When the host computer 110 reads data, the fixed-length data access mechanism 114 reads fixed-length data from the logical volume 200b, that is, the physical volume 128, and reads the data. The variable-length data is extracted by the mat conversion mechanism 112. When writing data, variable format data is converted into fixed length data by the format conversion mechanism 112, and fixed length data is converted by the fixed length data access mechanism 114. Write to logical volume 200b, ie, physical volume 128.

 The point here is that the format conversion mechanisms 124 and 112 perform the format conversion by the same method. In this way, the fixed-length data converted by one format conversion mechanism can be restored to a variable length by the other format conversion mechanism. You.

Also, by applying the RAID technology to the storage system 150 handled by the present invention, one physical volume 128 can be configured from a partial area of a plurality of storage devices. In this case, it is necessary to map the address on the physical volume 128 to the storage device that constitutes the RAID. Note that the logical volumes 200a and 200b and the physical volume 128 are uniquely numbered, and the logical volume 200a or If a logical volume 20b number is specified, the corresponding physical volume 1 2 8 is decided.

 Next, an example of the configuration of the logical volume 200 and the physical volume 128 will be described with reference to FIG. Each volume has the same basic configuration, and in the following description, these volumes are collectively referred to as storage devices. Storage device 400 is a rotating storage medium and a plurality of storage devices. It is composed of a disk 410 and a number of heads 413 equal to the number of disks 410. When the disk 4 10 rotates, the area of the disk 4 10 that one head 4 13 can access is referred to as the track 4 11 and the area of all the heads 4 13 The cylindrical set of tracks 411 passing below is called cylinder 412. The cylinders 4 12 are numbered in ascending order from 0 from the outermost circumference to the inner circumference, and the heads 4 13 are also numbered in ascending order from 0 from top to bottom. Therefore, the track 411 can be identified by the combination of the cylinder number and the head number. A special mark, called index 504, has been added to track 411 to identify the beginning of track 211.

 The logical volume 200 and the physical volume 128 have the same basic configuration as described above, but depending on whether the format is variable-length format or fixed-length format. However, the address expression on the storage device 400 and the storage format of the data are different. First, the data storage format in the case of a logical volume 200a, which is a variable-length volume, will be described with reference to FIG.

The track 4111 is composed of one home address (hereinafter abbreviated as HA) 5110 and one or more records 500. HA 510 is the first field located at the beginning of each track 411. Each record 500 is composed of one or more fields: a count section 501, a data section 502, and, in some cases, a key section before the data section. (Not shown). The count section 501 is a fixed-length field. The address of the record 500 is followed by the length of the following fields (the data section 502 and the key section described above). And so on. It is allowed that each record 500 has a variable length, that is, the length of the data section 502 may be different for each record 500. For this purpose, the count section 501 has the record key The length of the record and data sections 502 is stored, and if you look at the count section 501, you can see the length of each field of the record 500. Is in use. The address of record 500 is indicated by a combination of a cylinder number, a head number, and a record number, that is, a sequential number assigned from the beginning of the track.

 Next, the address expression of the logical volume 200b and the physical volume 128, which are fixed-length volumes, will be described with reference to FIG. In the fixed-length storage device 400, each track 411 is composed of a predetermined fixed-length area (hereinafter referred to as a block 600). Block 600 is uniquely numbered in storage device 400. Therefore, when accessing a certain area of the storage device 128, it is sufficient to specify the number of the first block 600 and the number of subsequent blocks 600 in the area.

 Next, a method of format-converting a variable-length logical volume 200a into a fixed-length physical volume will be described with reference to FIG.

 For format conversion, each track 411 represented by a variable-length format is divided into areas equal to the size of fixed-length block 600. Then, to the first block 600 represented by the number 0, the first area of the first track 411 represented by the cylinder number 0 and the head number 0 is allocated. Thereafter, the subsequent area on track 411 is allocated to the following block 600, and when the entire area of the first track 411 is allocated, the subsequent block is allocated. The next track, that is, the leading area of the track 41 1 of the cylinder number 0 and the head number 1 is assigned to the lock 600. In the same manner, the entire area of each track 411 is associated with each block 600.

 Since the length of each track is fixedly determined by the type of the logical volume 200a, the following equation is used to derive the track 411 from the track address. The number of the first block 600 stored and the number of blocks 600 per track can be obtained.

 (Equation 1) Number of blocks per track = <track capacity ÷ block capacity>

(Equation 2) Block number at the beginning of the track = (Cylinder number X head Number of heads + number of heads) X Number of subblocks per track where X> is the smallest integer greater than or equal to X.

 For example, if the capacity of sub-block 340 is 5 12 bytes, the capacity of track 211 is 47 KB, and the number of heads is 15, the track hits The number of sub-blocks is 94, and the first sub-block of cylinder number 0 and head number 1 track 41 1 is 94, cylinder number 100 and head number 41. The first sub-blocks of the track 411 of the node number 5 are 141 and 470.

 According to the above method, all areas of the logical volume 200a are allocated to the physical volume 128, but the format conversion shown here is only an example. It is. In general, various format conversion methods are conceivable, but what is important in the present invention is that a certain format conversion is performed by a format that all the host computers 110 have. This is to be recognized and used by the format conversion mechanism 124 of the control unit 120 and the control unit 120 of the control device 120.

 Next, the processing of the control device 120 in response to an input / output request from the host computer 100 will be described with reference to FIG. When the controller 120 receives an I / O request from the host computer 100, it obtains the number of the physical volume 128 corresponding to the specified logical volume 200a (Step 8 8 0). Next, in step 800, using (Equation 1) and (Equation 2), the block number and the block number on the physical volume 128 in which the track to be accessed is stored are stored. Find the number of clicks. Next, in step 810, it is checked whether or not the target track 411 is present in the cache 213, and if not, the relevant track 411 is checked. Is loaded from the physical volume 128 to the cache 123 (step 820).

If the target track 4 11 1 exists on the cache 12 3, the step 8 20 is skipped. Subsequently, in step 8330, the count section 501 of the first record 500 of the track 4111 is accessed, and the record 50 0 to be accessed is accessed in step 840. Check for 0. Here, step 840 is realized by the following method. That is, the control device 120 sets the address to be accessed designated by the host computer 100, that is, the cylinder number, head number, and record number as initial values, and then sets It holds the address to be accessed and compares it with the address read from the count section 501. If the result of the comparison is a match, the record to be accessed is 500, and the address to be accessed next is set.

 If the record 500 is to be accessed, the specified field is accessed from the host computer 100 in step 850. In other words, if the read access is used, the designated field is transferred from the cache 123 to the host computer 100 using the variable-length data access mechanism 121, and if the write access is used, Writes the specified field from the host computer 100 to the cache 123.

 When the access to the specified field is completed, it is determined by the CCW chain whether or not the host computer 100 requests access to the following record 500 ( Step 860). If so, read the count section 501 of the next record 500. Similarly, if the record 500 is not an access target at step 840, the record 500 is skipped, and the next record 500 is counted at step 870. Read out the port section 501. Thereafter, the process returns to step 840 again to check whether or not the record 500 is to be accessed.

 The processing from step 840 to step 870 is repeated until the access request from the host computer 100 ends.

 When the access request from the host computer 100 is a write request, the write data is stored on the cache 123. For this reason, the data must be written from the cache 123 to the physical volume 128, but this is easy to realize. That is, as obtained in step 800, the address of the track 41 1 is changed to the address on the physical volume 128 by using (Equation 1) and (Equation 2). That is, the first block number and the number of blocks are calculated. It is sufficient to write to the physical volume 128 using the storage device access mechanism 126 according to the address.

The method of accessing the logical volume 200a from the host computer 100 has been described above. Hereinafter, a method for sharing the storage device 400 between the host computers 100 and 110 will be described. For this purpose, the host computer 110 converts the physical volume 128 to the logical volume 200 b Therefore, the address on the logical volume 200b and the address on the physical volume 128 match. The host computer 110 accesses the physical volume 128 to read fixed-length data, and the format conversion mechanism 112 reads the fixed-length data from the read fixed-length data. The target variable-length record 500 is extracted. The format conversion mechanism 112 in the host computer 110 is composed of a variable length format and a fixed length format realized by the format conversion mechanism 124 of the controller 120. Since it knows how to embed the data in the data, it performs the same processing as the format conversion mechanism 124 to access the target variable-length record from the fixed-length data. can do. The details of this realization method will be described below with reference to FIGS. 7 and 8.

When the format conversion mechanism 112 receives the CCW chain created by the file access mechanism 113, the format conversion mechanism 112 interprets the CCW chain and determines whether it is a read access or a write access. to decide. First, the processing in the case of read access will be described with reference to FIG. Since the control unit 120 executes the association between the logical volume 200b and the physical volume 128, in the case of an access request to the logical volume 200b, step 880 is performed. It becomes unnecessary. Next, in step 800, the address to be accessed, that is, a cylinder number, a head number, and a record number, are obtained from the CCW chain. Using 2), obtain the block number and the number of blocks in which the track 4 11 1 to be accessed is stored. Next, in step 810, it is determined whether or not the target track 411 is stored in a cache (not shown) on the host computer 110. Here, the cache is a memory residing on the host computer 110, and may be, for example, a buffer defined only for this purpose, or a cache. This may be achieved using a unit. If the desired track 411 is not on the cache, the storage system 150 is accessed in step 820 to cache the track 411. Read to When reading track 4111 from the storage system 150, a read SCSI command is generated based on the block number and block number obtained in step 800. The fixed-length data access mechanism 1 1 4 Is executed. Thereafter, the format conversion mechanism 112 executes steps 830 to 870 in accordance with the content of the CCW chain, but this is the same as that described above, and a description thereof will be omitted.

 Next, the format conversion mechanism 112 analyzes the CCW chain created by the file access mechanism 113, and as a result, describes the processing in the case of write access, with reference to FIG. I do. In FIG. 8, the processing of steps 900, 930, 940, 950, 960, and 970 is the same as the processing of steps 800, 830, and 8 in FIG. The processing is completely the same as the processing of 40, 850, 860, and 870, so the description will be omitted, and the remaining steps will be described.

 At step 920, the area specified by the block number and the number of blocks obtained at step 900 is stored in the storage device system 1 via the fixed-length data access mechanism 114. Read from 0. Next, at step 930 to step 970, the CCW chain is analyzed, and when all of the requested record 300 updates have been completed in the cache, step 930 is executed. At 80, the relevant track 4111 is written to the storage system 150 again via the fixed-length data access mechanism 114.

 Next, the processing of the control device 120 when there is access from the host computer 110 will be described with reference to FIG. The point of processing by the control unit 120 is to access the data stored in the physical volume 128 by using the SCSI command as it is without performing format conversion. It is to make it. The host computer 110 extracts variable-length data from the fixed-length data read from the storage system 150 by the format conversion mechanism 112, and converts the variable-length data to fixed-length data. Convert to data and write to storage system 150.

First, in step 1000, the host computer 110 obtains a physical volume 128 corresponding to the specified logical volume 200b. Then, the access address, that is, the block number and the number of blocks, from the host computer 110 to the specified logical volume 200 b are converted to the physical volume 128. Access address. Next, at step 1010, it is determined whether or not the access is a read access, and if so, at step 102, whether the desired data is present in the cache 123 is determined. Check if it exists For example, at step 1303, the target data is loaded to the cache 123 using the storage device access mechanism 126. Then, in step 104, the read data is transferred to the host computer 110, and the processing is completed. If write access is determined in step 110, write data is received from the host computer 110 and stored in the cache 123 to complete the processing. After that, it is necessary to write the data from the cache 123 to the physical volume 128, but in this case, the write address specified by the host computer 110 is used to write the data. Since the address is still on the physical volume 128, the number of the logical volume 200b is converted to the number of the physical volume 128, and then to that address. Just write it.

 According to the above processing, the variable-length data written from the host computer 100 is converted into fixed-length data by the format conversion mechanism 124, and the physical volume 1 Written to 28. When reading that data from the host computer 110, the host computer 110 specifies the address on the physical volume 128 that stores the data, and the fixed-length data Read it out. Then, the target variable length data is extracted by the format conversion mechanism 112.

 On the other hand, when the host computer 110 writes data, the format conversion mechanism 112 converts the variable-length data into fixed-length data and converts the physical volume 1 into the fixed-length data. 2 Write to 8. When the host computer 100 reads the data, the address on the logical volume 200 a where the data is stored is specified, and the control device 120 specifies the address. Converts the address to the address on physical volume 128 and reads fixed-length data. Then, the format conversion mechanism 124 extracts the variable-length data and transfers the data to the host computer.

By these processes, the storage device between the host computer 100 having a variable-length access interface and the host computer 110 having a fixed-length access interface is stored. Data stored in the system 150 can be shared. Industrial applicability As described above, the method of sharing data in a plurality of host computers according to the present invention is useful as a method of sharing data between a plurality of host computers having different access interfaces, and is fixed. The data of the storage device formatted in the fixed-length format is shared between the host computer having the long-term access interface and the host computer having the variable-length access interface. It is suitable for building computer systems that perform

Claims

The scope of the claims 1. a first computer having an interface for accessing a first logical volume formatted by a variable-length format;  An interface for accessing the second logical volume formatted by the fixed-length format and a predetermined logic from the fixed-length data read from the second logical volume. A second computer having means for extracting the variable-length data and converting the variable-length data into fixed-length data to be written into the second logical volume according to the predetermined logic; and A physical volume formatted by the format, connected to the first and second computers and the physical volume, and the first logical volume is connected to the predetermined logical volume; The format is converted into the physical volume formatted according to the logic according to the fixed-length format, and the second logical volume and the physical volume card are converted. Less The computer system composed of a controller to attach corresponds allowed Itasa. 2. a first computer having a write interface to the first logical volume formatted according to the variable length format;  A read interface to the second logical volume formatted by the fixed-length format, and a read from the second logical volume. A second computer having means for extracting variable-length data from the fixed-length data according to predetermined logic,  The physical volume formatted by the fixed-length format is connected to the first and second computers and the physical volume, and the first logical volume is connected to the predetermined logical volume. The format is converted into the physical volume formatted by the fixed-length format according to the logic, and the address of the second logical volume and the address of the physical volume are converted. A computer system consisting of a control unit that matches and matches  3. a first computer having a read interface to the first logical volume formatted by the variable length format; The write interface to the second logical volume formatted by the fixed-length format and the variable-length data are written in the second logical volume according to the predetermined logic. Means for converting to fixed length data to be written to the volume, A second calculator having  The physical volume formatted by the fixed-length format is connected to the first and second computers and the physical volume, and the first logical volume is connected to the predetermined logical volume. The format is converted to the physical volume formatted by the fixed-length format according to the logic of the second logical volume and the physical volume of the second logical volume. A computer system consisting of a control unit that matches the addresses. 4. a first computer having an access interface to a first logical volume formatted according to a variable length format;  The access interface to the second logical volume formatted by the fixed-length format and the fixed-length data read from the second logical volume. A second variable having a variable-length to fixed-length format conversion function of extracting variable-length data, converting the variable-length data into a fixed-length format, and writing the converted data into the second logical volume. A calculator,  A physical volume formatted by a fixed-length format, connected to the first and second computers and the physical volume, and the variable-length to fixed-length format conversion. Having a function of storing the data of the first logical volume in the physical volume and using the data of the second logical volume. A computer system configured to associate an address with an address of the physical volume to thereby receive a control device for accessing the physical volume from the second computer. .