Patent Publication Number: US-2023153009-A1

Title: Data replication system and data replication method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 17/474,500 filed Sep. 14, 2021, which claims the benefit of priority from Japanese Patent Application No. 2021-117972, filed Jul. 16, 2021, the entire contents of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a data replication system and a data replication method. 
     Description of the Related Art 
     For data processing of a storage system, a technique is described in National Publication of International Patent Application No. 2014-524601 (Patent Literature 1). In this publication, there is the description “A first storage system includes a first RAID group configured by a plurality of first storage devices on which a first logical volume is based. A second storage system includes a second RAID group configured by a plurality of second storage devices on which a second logical volume is based. A RAID configuration of the first RAID group and a RAID configuration of the second RAID group are the same. A type of a compression/decompression function of the first storage devices and a type of a compression/decompression function of the second storage devices are the same. For data in the first logical volume, compressed data is read from the first storage device without being decompressed. The read compressed data is written in the second storage device present in the same position as the position in the first storage device in the second RAID group”. 
     According to Patent Literature 1, it is possible to reduce an amount of data transmitted and received between the storage systems. However, this technique cannot be applied when compression schemes are different between the first storage system and the second storage system. The second storage system is desired to be configured with reduced processing performance compared with the first storage system. Therefore, it has been demanded to realize replication having high versatility applicable even when there are differences of compression schemes and performance between the storage systems and capable of suppressing a communication amount. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to realize replication having high versatility and capable of suppressing a communication amount. 
     In order to achieve the object, representative one data replication system of the present invention includes: a first storage system including a processor and providing a primary site; and a second storage system including a processor and providing a secondary site. The first storage system compresses data relating to read and write by the primary site and stores the data in a first physical volume. The second storage system compresses data relating to read and write by the secondary site and stores the data in a second physical volume. When performing replication for transferring the data stored in the first physical volume of the first storage system to the second storage system and storing the data in the second physical volume, the first storage system and the second storage system determine, based on a compression scheme executable by the first storage system and a compression scheme executable by the second storage system, a compression scheme to be applied to transfer target data and transfer the transfer target data compressed by the determined compression scheme. 
     Representative one data replication method of the present invention is a data replication method performed by a data replication system including: a first storage system including a processor and configured to compress data relating to read and write by a primary site and store the data in a first physical volume; and a second storage system including a processor and configured to compress data relating to read and write by a secondary site and store the data in a second physical volume. The data replication method including: a step in which the first storage system compresses the data relating to read and write by the primary site with a first compression scheme and stores the data in the first physical volume; a step in which, when performing replication for transferring the data stored in the first physical volume of the first storage system to the second storage system and storing the data in the second physical volume, the first storage system and the second storage system determine, based on a compression scheme executable by the first storage system and a compression scheme executable by the second storage system, a compression scheme to be applied to transfer target data; and a step in which the first storage system and the second storage system transfer the transfer target data compressed by the determined compression scheme. 
     According to the present invention, it is possible to realize replication having high versatility and capable of suppressing a communication amount. Problems, configurations, and effects other than those described above are clarified by the following explanation of embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a configuration diagram of a data replication system according to a first embodiment; 
         FIG.  2    is an explanatory diagram of a primary storage in the first embodiment; 
         FIG.  3    is an explanatory diagram of a secondary storage in the first embodiment; 
         FIG.  4    is an explanatory diagram about compression and data storage in the primary storage; 
         FIG.  5    is an explanatory diagram about decompression and recompression in the primary storage; 
         FIG.  6    is an explanatory diagram about compression and data storage in the secondary storage; 
         FIG.  7    is a sequence chart for explaining a processing operation of replication in the first embodiment; 
         FIG.  8    is an explanatory diagram of a primary storage in a second embodiment; 
         FIG.  9    is an explanatory diagram of a secondary storage in the second embodiment; 
         FIG.  10    is a sequence chart for explaining a processing operation of replication in the second embodiment; 
         FIG.  11    is an explanatory diagram of the operation of a logical/physical-address managing unit in the second embodiment; 
         FIG.  12    is a first modification of a system configuration; and 
         FIG.  13    is a second modification of the system configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention are explained below with reference to the drawings. 
     First Embodiment 
       FIG.  1    is a configuration diagram of a data replication system according to a first embodiment. The data replication system shown in  FIG.  1    includes a first storage system that provides a primary site and a second storage system that provides a secondary site. 
     Specifically, the data replication system has a configuration in which a primary server  100  and a primary storage  200  are connected to a network  510 , a secondary server  300  and a secondary storage  400  are connected to a network  520 , and the network  510  and the network  520  are connected. 
     Note that the primary server  100  and the network  510  are connected by a communication line  500 . The primary storage  200  and the network  510  are connected by a communication line  501 . The secondary server  300  and the network  520  are connected by a communication line  502 . The secondary storage  400  and the network  520  are connected by a communication line  503 . 
     The primary server  100  is a server that issues an I/O on the primary site side. 
     The primary storage  200  is a storage for data storage on the primary site side and includes a primary volume  10 . The primary storage  200  operates as a storage that retains master data in the data replication system. 
     The secondary server  300  is a server that issues an I/O on the secondary site side. 
     The secondary storage  400  is a storage for data storage on the secondary site side and includes a secondary volume  11 . The secondary storage  400  operates as a storage that retains replicated data in the data replication system. 
       FIG.  2    is an explanatory diagram of the primary storage  200  in the first embodiment. As shown in  FIG.  2   , the primary storage  200  includes a network interface  201 , a logical volume  210 , a physical volume  211 , a first compressing unit  220 , a decompressing unit  230 , a second compressing unit  231 , a logical/physical-address managing unit  240 , and a compression-scheme managing unit  250 . 
     When write by the primary site is processed, the network interface  201  receives a write request via the communication line  501  and writes data in the logical volume  210 . The data written in the logical volume  210  is compressed by the first compressing unit  220  and written in the physical volume  211  as compressed data. 
     When read by the primary site is processed, the network interface  201  receives a read request via the communication line  501  and reads compressed data  212  from the physical volume  211 . The read compressed data is decompressed by the decompressing unit  230  to be decompressed data  235  and is written in the logical volume  210  to enable a read response. 
     When data in the physical volume  211  is transmitted to the secondary storage  400  and replication is performed, target compressed data is read from the physical volume  211  and decompressed by the decompressing unit  230  to be the decompressed data  235  and, thereafter, compressed by the second compressing unit  231  and transmitted to the secondary storage  400  as compressed data  232 . 
     The logical/physical-address managing unit  240  includes a management table in which a logical address of the logical volume  210  and a physical address to be stored in the physical volume  211  are mapped. When write in the physical volume  211  is performed, a physical address  241  is generated every time and passed to the physical volume  211 . 
     The compression-scheme managing unit  250  manages compression and decompression processing in the primary storage  200 . A compression algorithm used by the first compressing unit  220 , that is, a main algorithm used when generating compressed data to be stored in the physical volume  211  is represented as a first compression algorithm for convenience. On the other hand, a main algorithm used by the secondary storage  400 , which is a replication destination, when storing data relating to read and write by the secondary site in the physical volume is represented as a second compression algorithm for convenience. Note that the first and second compression algorithms are not defined by a storage that uses the first and second compression algorithms. For example, the second compression algorithm is sometimes used in the primary storage  200  as explained below. A plurality of compression algorithms is present in the first compression algorithm or the same compression algorithm is included in the first compression algorithm and the second compression algorithm. 
     The compression-scheme managing unit  250  outputs a compression scheme designation signal  251  for designating the first compression algorithm and a compression scheme designation signal  252  for designating the second compression algorithm to control a compression algorithm in use. Specifically, the compression-scheme managing unit  250  gives the compression scheme designation signal  251  to the first compressing unit  220  and gives the compression scheme designation signal  252  to the second compressing unit  231 . 
     A plurality of algorithms usable by the second compressing unit  231  may be present. In this case, the second compression algorithm is selected according to a replication destination. 
       FIG.  3    is an explanatory diagram of the secondary storage  400  in the first embodiment. As shown in  FIG.  3   , the secondary storage  400  includes a network interface  401 , a logical volume  410 , a physical volume  411 , a compressing unit  420 , and decompressing unit  430 , a selecting unit  453 , a logical/physical-address managing unit  440 , and a compression-scheme managing unit  450 . 
     When the network interface  401  receives the compressed data  232  from the primary storage  200 , the compressed data  232  is directly stored in the physical volume  411  via the selecting unit  453 . This is because, since the compressed data  232  is compressed by the second compression algorithm used by the secondary storage  400 , it is unnecessary to decompress and recompress the compressed data  232 . 
     For example, when an abnormality occurs in the primary storage  200  and the secondary storage  400  processes write by the secondary site, the network interface  401  receives a write request via the communication line  503  and writes data in the logical volume  410 . The data written in the logical volume  410  is compressed by the compressing unit  420 . At this time, the compressing unit  420  uses the second compression algorithm. The compressed data is written in the physical volume  411  via the selecting unit  453 . 
     When read by the secondary site is processed, the network interface  401  receives a read request via the communication line  503 . The compressed data  232  is read from the physical volume  411 . The read compressed data is decompressed by the decompressing unit  430  to be decompressed data and is written in the logical volume  410  to enable a read response. 
     The logical/physical-address managing unit  440  includes a management table in which a logical address of the logical volume  410  and a physical address to be stored in the physical volume  411  are mapped. When write is performed in the physical volume  411 , a physical address  441  is generated every time and passed to the physical volume  411 . 
     The compression-scheme managing unit  450  manages compression and decompression processing in the secondary storage  400 . The secondary storage  400  does not need to perform compression processing in replication and performs the compression processing when write by the I/O of the secondary site is performed during failover. The compression-scheme managing unit  450  gives a control signal  452  to the selecting unit  453  to switch processing at a replication time and processing at a write time by the I/O. 
       FIG.  4    is an explanatory diagram about compression and data storage in the primary storage  200 . In  FIG.  4   , first, data of a logical address A and data of a logical address B are stored in the logical volume  210 . In the logical volume  210 , both of the data of the logical address A and the data of the logical address B have 16 KB length. 
     The first compressing unit  220  compresses the data of the logical address A with a first compression algorithm L1 and generates compressed data A. A size of the compressed data A is reduced to 4 KB length by the compression. 
     Similarly, the first compressing unit  220  compresses the data of the logical address B with the first compression algorithm L1 and generates compressed data B. A size of the compressed data B is reduced to 8 KB length by the compression. 
     The compressed data A and the compressed data B are written in continuous addresses of the physical volume  211 . By compressing the data on the logical volume  210  and writing the compressed data in the continuous addresses in this way, it is possible to efficiently use a data capacity of the physical volume  211 . 
       FIG.  5    is an explanatory diagram about decompression and recompression in the primary storage  200 . In replication, first, the compressed data A and the compressed data B are read from the physical volume  211 . The compressed data A and the compressed data B read from the physical volume  211  are in a state in which the compressed data A and the compressed data B are compressed by the first compression algorithm L1. Therefore, the compressed data A and the compressed data B are referred to as first compressed data A and first compressed data B. The first compressed data A and the first compressed data B are specific examples of the compressed data  212  shown in  FIG.  2   . 
     The decompressing unit  230  performs decompression processing of the first compressed data A based on the first compression algorithm L1. Decompressed data obtained by the decompression is the data of the logical address A. 
     Similarly, the decompressing unit  230  performs decompression processing of the first compressed data B based on the first compression algorithm L1. Decompressed data obtained by the decompression is the data of the logical address B. 
     The second compressing unit  231  recompresses the decompressed data. The second compressing unit  231  corresponds to a plurality of second compression algorithms. In  FIG.  5   , second compression algorithms L2a and L2b are illustrated. The second compressing unit  231  selects a second compression algorithm according to a secondary storage at a replication destination. In the following explanation, it is assumed that the secondary storage  400  at the replication destination uses the second compression algorithm L2a. 
     The second compressing unit  231  recompresses the data of the logical address A with the second compression algorithm L2a and generates compressed data. The compressed data is referred to as second compressed data A. 
     Similarly, the second compressing unit  231  recompresses the data of the logical address B with the second compression algorithm L2a and generates compressed data. The compressed data is referred to as second compressed data B. 
     The second compressed data A and the second compressed data B are combined to be a specific example of the compressed data  232  shown in  FIG.  2   . 
       FIG.  6    is an explanatory diagram about compression and data storage in the secondary storage  400 . In  FIG.  6   , first, the data of the logical address A and the data of the logical address B are stored in the logical volume  410 . In the logical volume  410 , both of the data of the logical address A and the data of the logical address B have 16 KB length. 
     The second compressing unit  420  compresses the data of the logical address A with the second compression algorithm L2a and generates the second compressed data A. A size of the second compressed data A is reduced to 8 KB length by the compression. 
     Similarly, the second compressing unit  420  compresses the data of the logical address B with the second compression algorithm L2a and generates the second compressed data B. A size of the second compressed data B is reduced to 8 KB length by the compression. 
     The second compressed data A and the second compressed data B are combined and written in the physical volume  411  via the selecting unit  453 . 
     On the other hand, the compressed data  232  received from the primary storage  200  at a replication time is in a state in which the compressed data  232  is already compressed by the second compression algorithm L2a. Therefore, the compressed data  232  is directly written in the physical volume  411  via the selecting unit  453  without being decompressed and recompressed. 
       FIG.  7    is a sequence chart for explaining a processing operation of replication in the first embodiment. First, the primary storage  200  transmits a secondary storage storing method acquisition command to the secondary storage  400  ( 1000 ). The secondary storage  400  notifies a secondary storage storing method, that is, a compression algorithm used by the secondary storage  400  to the primary storage  200  ( 1001 ). The primary storage  200  determines, as a compression algorithm of data to be transferred, a compression algorithm usable by the primary storage  200  and the secondary storage  400  in common. When the compression algorithm of the data to be transferred is a compression algorithm used at a primary storage storing time, decompression and recompression explained below (steps S 103  and S 104 ) can be omitted. Otherwise, the decompression and the recompression explained below are performed such that the data can be compressed and decompressed by the secondary storage  400 . When a compression algorithm usable in common is absent, the primary storage  200  performs only the decompression (step S 103 ) and the secondary storage  400  performs the recompression (step S 104 ) using a compression algorithm usable by the secondary storage  400 . These kinds of processing are performed, for example, at a system construction time or a replication setting time. The notified compression algorithm of the secondary storage  400  is managed by the primary storage  200 . Thereafter, the subsequent replication processing is periodically executed. 
     In the replication processing, first, the primary storage  200  selects replication target data (step S 101 ). For example, the primary storage  200  only has to select a difference from the last replication as a target. 
     After step S 101 , the primary storage  200  reads the data selected as the target from the physical volume  211  (step S 102 ), decompresses the data based on the first compression algorithm (step S 103 ), and recompresses the data with the second compression algorithm (step S 104 ). 
     The primary storage  200  transfers compressed data generated by the recompression to the secondary storage  400  ( 1002 ). 
     The secondary storage  400  allocates a physical address to the compressed data received from the primary storage  200  (step S 201 ), stores the compressed data in the physical volume  411  (step S 202 ), and notifies a copy end to the primary storage  200  ( 1004 ). 
     Note that processing for notifying the copy end after storing the compressed data in the physical volume  411  is illustrated above. However, the secondary storage  400  may be configured to store the compressed data received from the primary storage  200  in a cache, notify the copy end to the primary storage  200 , and, thereafter, store the compressed data in the physical volume  411 . 
     Second Embodiment 
       FIG.  8    is an explanatory diagram of the primary storage  200  in a second embodiment. As shown in  FIG.  2   , the primary storage  200  includes the network interface  201 , the logical volume  210 , the physical volume  211 , the first compressing unit  220 , the decompressing unit  230 , the logical/physical-address managing unit  240 , and the compression-scheme managing unit  250  but does not include the second compressing unit  231 . 
     When transmitting data in the physical volume  211  to the secondary storage  400  and performing replication, the primary storage  200  in the second embodiment reads the target compressed data  212  from the physical volume  211  and directly transmits the target compressed data  212  to the secondary storage  400 . That is, in the second embodiment, data for replication is transmitted while keeping a state in which the data is compressed by the first compression algorithm. 
     Explanation about the other operations is omitted because the other operations are the same as the operations in the first embodiment. 
       FIG.  9    is an explanatory diagram of the secondary storage  400  in the second embodiment. As shown in  FIG.  9   , the secondary storage  400  includes the network interface  401 , the logical volume  410 , the physical volume  411 , the compressing unit  420 , and decompressing unit  482 , a selecting unit  473 , a logical/physical-address managing unit  480 , and a compression-scheme managing unit  470 . 
     When the network interface  401  receives the compressed data  212  from the primary storage  200 , the compressed data  212  is directly stored in the physical volume  411  via the selecting unit  473 . The compressed data  212  is compressed by the first compression algorithm used by the primary storage  200 . 
     For example, when an abnormality occurs in the primary storage  200  and the secondary storage  400  processes write by the secondary site, the network interface  401  receives a write request via the communication line  503  and writes data in the logical volume  410 . The data written in the logical volume  410  is compressed by the compressing unit  420 . At this time, the compressing unit  420  uses the second compression algorithm. The compressed data is written in the physical volume  411  via the selecting unit  473 . 
     When read by the secondary site is processed, the network interface  401  receives a read request via the communication line  503  and the compressed data is read from the physical volume  411 . 
     The read compressed data is decompressed by the decompressing unit  482  to be decompressed data and is written in the logical volume  410  to enable a read response. An algorithm used for the decompression is different depending on the read compressed data. However, it only has to be decided according to a control signal  481  from the logical/physical-address managing unit  480  which algorithm is used. 
     The logical/physical-address managing unit  480  includes a management table in which a logical address of the logical volume  410  and a physical address to be stored in the physical volume  411  are mapped. When data is written in the physical volume  411 , the physical address  441  is generated every time and passed to the physical volume  411 . 
     Further, the logical/physical-address managing unit  480  associates a flag for specifying a compression algorithm with a physical address and manages the physical address. When data is read from the physical volume  411 , the logical/physical-address managing unit  480  refers to the flag and notifies the control signal  481  for designating the compression algorithm corresponding to the physical address to the decompressing unit  482 . 
     The compression-scheme managing unit  470  manages compression and decompression processing in the secondary storage  400 . The secondary storage  400  does not need to perform compression processing in replication and performs the compression processing when performing write by the I/O of the secondary site during failover. The compression-scheme managing unit  470  gives a control signal  472  to the selecting unit  473  to switch processing at a replication time and processing at a write time by the I/O. The compression-scheme managing unit  470  notifies a compression scheme of data written in the physical volume  411  to the logical/physical-address managing unit  480  and causes the logical/physical-address managing unit  480  to register the compression scheme in the management table. Note that the compression processing can be simply performed in the replication. 
       FIG.  10    is a sequence chart for explaining a processing operation of replication in the second embodiment. First, the secondary storage  400  transmits a primary storage storing method acquisition command to the primary storage  200  ( 1100 ). As in the first embodiment, the primary storage  200  determines a compression algorithm of data to be transferred and notifies a primary storage storing method, that is, a compression algorithm used by the primary storage  200  to the secondary storage  400  ( 1101 ). In this embodiment, communication may be added and the secondary storage  400  may determine a compression algorithm of data to be transferred. These kinds of processing are performed, for example, at a system construction time or a replication setting time. The notified compression algorithm of the primary storage  200  is managed by the secondary storage  400 . Thereafter, the subsequent replication processing is periodically executed. 
     In the replication processing, first, the primary storage  200  selects replication target data (step S 301 ). For example, the primary storage  200  only has to select a difference from the last replication as a target. 
     After step S 301 , the primary storage  200  reads the data selected as the target from the physical volume  211  (step S 302 ) and transfers the data to the secondary storage  400  ( 1102 ). If necessary, decompression and recompression (steps S 103  and S 104 ) are performed as in the first embodiment. 
     The secondary storage  400  allocates a physical address to compressed data received from the primary storage  200  (step S 401 ). Since write by replication is performed, the logical/physical-address managing unit  480  associates a flag indicating a compression scheme used by the primary storage with the physical address (step S 402 ). Thereafter, the logical/physical-address managing unit  480  stores the data in the physical volume  411  (step S 403 ) and notifies a copy end to the primary storage  200  ( 1104 ). 
     Note that processing for notifying the copy end after storing the compressed data in the physical volume  411  is illustrated above. However, the secondary storage  400  may be configured to store the compressed data received from the primary storage  200  in a cache, notify the copy end to the primary storage  200 , and, thereafter, store the compressed data in the physical volume  411 . 
       FIG.  11    is an explanatory diagram of the operation of the logical/physical-address managing unit  480  in the second embodiment. When write in the physical volume  411  occurs, the logical/physical-address managing unit  480  determines whether the write is writing by replication (step S 501 ). 
     If the write is writing by replication (step S 501 ; Yes), the logical/physical-address managing unit  480  selects a primary storage storing scheme, that is, a compression algorithm used by the primary storage  200  (step S 502 ). 
     If the write is not writing by replication (step S 501 ; No), the logical/physical-address managing unit  480  selects a secondary storage storing scheme, that is, a compression algorithm used by the secondary storage  400  (step S 503 ). 
     The logical/physical-address managing unit  480  associates a flag for specifying the selected storage scheme with a physical address and manages a correspondence relation between a logical address and the physical address (step S 504 ). 
     (Modifications) 
     Variations of a system configuration are explained. 
       FIG.  12    is a first modification of the system configuration. In the configuration shown in  FIG.  12   , a primary storage  600  includes a processor  601 , a compression/decompression accelerator  602 , a memory  603 , and a storage medium  604 . 
     On the other hand, in the configuration shown in  FIG.  12   , a secondary storage  700  includes a processor  701 , a memory  702 , and a storage medium  703  but does not include a compression/decompression accelerator. The processor  701  performs compression and decompression in software processing. 
     In this way, the primary storage  600  realizes high performance by including the processor  601  that processes read and write by the primary site and the compression/decompression accelerator  602  that processes compression and decompression. The secondary storage  700  is configured to perform software processing of compression and decompression and reduces cost. 
     Therefore, differences occur in configurations and performance between the primary storage  600  and the secondary storage  700 . However, the present invention can be applied to even such a configuration. For example, when the compression and decompression processing is often performed in the primary storage  600  as in the first embodiment, decompression and recompression of data only have to be executed for replication making use of the high performance. When the compression and decompression processing is often performed on the secondary storage  700  side as in the second embodiment, the system only has to be configured to have high performance on the secondary storage side. 
       FIG.  13    is a second modification of the system configuration. In the configuration shown in  FIG.  13   , the configuration of the primary storage  600  is the same as the configuration shown in  FIG.  12   . However, the secondary site side is realized by a software definition type storage that uses Cloud  530 . In such a configuration, addition of functions on the secondary storage side is easy. A compression algorithm to which the primary storage  600  is not adapted is considered to be usable. However, replication by compressed data can be realized by decompressing, on the secondary storage side, according to necessity, data compressed by the primary storage. 
     As explained above, the data replication system disclosed in the embodiments includes a first storage system including a processor and providing a primary site and a second storage system including a processor and providing a secondary site. The first storage system compresses data relating to read and write by the primary site and stores the data in a first physical volume. The second storage system compresses data relating to read and write by the secondary site and stores the data in a second physical volume. When performing replication for transferring the data stored in the first physical volume of the first storage system to the second storage system and storing the data in the second physical volume, the first storage system and the second storage system determine, based on a compression scheme executable by the first storage system and a compression scheme executable by the second storage system, a compression scheme to be applied to transfer target data and transfer the transfer target data compressed by the determined compression scheme. 
     With such a configuration and an operation, it is possible to suppress a communication amount even between storage systems having different compression schemes. Since the second storage system does not need to decompress and recompress data received in replication, it is possible to reduce requests for processing performance. 
     According to the configuration of the first embodiment, the first storage system determines a compression scheme of the transfer target data, reads the compressed transfer target data from the first physical volume and performs decompression processing, and compresses the decompressed data with the determined compression scheme of the transfer target data and transfers it to the second storage system. The second storage system receives the data compressed by the second compression scheme and stores the data in the second physical volume. 
     Therefore, it is possible to reduce a processing load on the second storage system side. The second storage system side does not need to be adapted to the compression scheme used in the first storage system. 
     Note that, when the compression scheme of the data stored in the first storage system is not possible in the second storage system, the decompression and the compression may be performed. 
     According to the configuration of the second embodiment, when the first storage system determines to transfer the transfer target data with the stored compression scheme, the first storage system reads the transfer target data from the first physical volume and transmits the transfer target data to the second storage system while keeping the compressed state. The second storage system receives the compressed data and stores the compressed data in the second physical volume and, when read and write for the data are necessary, performs decompression processing corresponding to the first compression scheme. 
     Therefore, it is possible to reduce a processing load on the first storage system side. The first storage system side does not need to be adapted to a compression scheme used in the second storage system. 
     Decompression of data relating to replication is limited to a time when read is necessary because of abnormality occurrence or the like. 
     Note that the second storage system is also capable of decompressing the received compressed data, compressing the data with a different compression scheme, and storing the data in the second physical volume. 
     Further, the second storage system may be configured to receive the compressed data and store the compressed data in the second physical volume and, when write for the data occurs, decompress the compressed data, compress the data with a different compression scheme, and store the compressed data in the second physical volume. 
     In the configuration of the first embodiment, the first storage system is adaptable to a plurality of compression schemes and can also be configured to select a compression scheme used in the second storage system at a replication destination and transmit data compressed by the compression scheme. 
     Therefore, it is possible to perform flexible processing adjusted to the configuration of the second storage system. 
     When the second storage system at the replication destination is adaptable to a plurality of compression schemes, a compression scheme applied when the transfer target data is transmitted to the second storage system may be determined based on a compression scheme applied when the transfer target data is stored in the first physical volume. For example, if the compression scheme applied when the transfer target data is stored in the first physical volume is usable in the second storage system as well, the transfer target data can be transmitted while being kept compressed by the first compression scheme. 
     The first storage system may separately include a processor configured to process read and write by the primary site and a processing unit configured to process compression and decompression. 
     In such a configuration, it is possible to achieve both of high processing performance in the primary site and a cost reduction as a whole. 
     The second storage system may be a software type storage system configured by a plurality of servers. 
     In such a configuration, it is possible to operate the second storage system flexibly and at low cost. 
     Note that the present invention is not limited to the embodiments explained above and includes various modifications. For example, the embodiments explained above are explained in detail in order to clearly explain the present invention and are not always limited to embodiments including all the explained components. Not only deletion of such components but also substitution and addition of components are possible. 
     REFERENCE SIGNS LIST 
       10 : primary volume,  11 : secondary volume,  100 : primary server,  200 : primary storage,  201 : network interface,  210 : logical volume,  211 : physical volume,  212 : compressed data,  220 : first compressing unit,  230 : decompressing unit,  231 : second compressing unit,  232 : compressed data,  235 : decompressed data,  240 : logical/physical-address managing unit,  241 : physical address,  250 : compression-scheme managing unit,  251 : compression scheme designation signal,  252 : compression scheme designation signal,  300 : secondary server,  400 : secondary storage,  401 : network interface,  410 : logical volume,  411 : physical volume,  420 : second compressing unit,  420 : compressing unit,  430 : decompressing unit,  440 : logical/physical-address managing unit,  441 : physical address,  450 : compression-scheme managing unit,  452 : control signal,  453 : selecting unit,  470 : compression-scheme managing unit,  472 : control signal,  473 : selecting unit,  480 : logical/physical-address managing unit,  481 : control signal,  482 : decompressing unit,  500 : communication line,  501 : communication line,  502 : communication line,  503 : communication line,  510 : network,  520 : network,  530 : Cloud,  600 : primary storage,  601 : processor,  602 : compression/decompression accelerator,  603 : memory,  604 : storage medium,  700 : secondary storage,  701 : processor,  702 : memory,  703 : storage medium